American and British English use formality in this fashion as well. The usage is in line with the definitions presented here, as - even in your Tarun / Tina example - a formality remains an imperative (a must-do). But, as with all must statements (except maybe logical entailment), there are implicit conditions and consequences: you must do this [if you don't want that].
If something is a formality, you must do it if you want to remain within the bounds of normal, accepted or polite societal laws, etiquette or customs. If you don't care about violating the rules or the attendant repercussions, then you've no need to mind formalities. Logically speaking, obeying a formality is always optional. But, sometimes the situation or consequences make it obvious that there's only one reasonable choice to make.
In your example, Tarun invites Tina to the wedding for formality's sake, even though he doesn't want her to come. He's obligated to do so because he does not want to be rude, disappoint his family, or for some other similar reason. The language of his invitation makes it clear that he doesn't want her to go, but because he did extend some sort of invitation, he's obeyed the letter of the [social] law, and if Tina complains, he can say that he did invite her. We might say he extended her the courtesy of an (admittedly false) invitation.
Here's another example. Consider the CEO of a company interviewing a promising candidate for a job. The hiring process is lengthy, involving multiple screenings and a fair amount of tax paperwork for the government. The CEO is blown away by the applicant and says:
You're hired! Don't worry about the final interview or filling out these forms, those are just formalities at this point.
This means that the applicant will be hired, and the last interview is now just a hollow observance necessary for adherence to company policy. Similarly for the forms, filling them out is needed to legally and officially begin the employment, but the CEO is saying you work here now to the interviewee. These things are formalities - they're obligatory for remaining in compliance with governing rules - but the results aren't in question (they normally would be) and if the consequences of breaking the rules weren't important, the formalities wouldn't be observed.
Short answer: a confusing something and a confused something are similar, and closely related, but not necessarily the same.
Let's try a simpler verb: interesting--interested. There are 3 people in this example, A, B, and C. Suppose that,
A interests B. -- Let's say that A successfully gets B's attention by making himself or herself look interesting. We can say that, B finds A interesting.
C may observe that,
- A is an interesting person (to B), and
- B is the interested person.
C may or may not think that B is interesting. However, if C thinks that the fact that B is interested in A makes B interesting, C may think that B is interesting, too, which in turn makes C think that,
- B is the interested person, and
- B is an interesting person.
In this case (to C), B is both interesting and interested.
The same applies to confusing and confused in your question.
When we say or write confusing ideas, we mean that to us, the ideas are confusing, and we look at it from our point of view. We feel that they are "confusing". To us, it's difficult to understand.
When we say or write confused ideas, we mean that the ideas are confused. They are not well organized or explained. We may say that the person who states the ideas "confuse" them, and as a result, the ideas are not clear or not easy to understand.
Thus, a confusing something may not be confused.
And a confused something may not be confusing, either.
In short, they're similar, and closely related, but not necessarily the same.
Best Answer
It depends on intonation. With a certain, emphatic intonation, Tom looks pretty tired can mean "Tom looks very tired; indeed, his level of tiredness is remarkable." With ordinary intonation, it just means "Tom is moderately tired—tired enough to matter, but his level of tiredness is not especially remarkable."
The emphatic intonation that I have in mind drags out each syllable of pretty to an equally long length, about as long as the word tired. The pitches go something like E D C, like "Three blind mice". Of course, there are many other kinds of intonations and emphasis that a person could give the words, suggesting many different kinds of tiredness, and there is no precise, standardized code. You just improvise.