Word Choice – Subtle Differences Between “To Study” and “To Learn”

Yes. Continuous means from some start to some end without break:

The water flowed continuously over the dam.

whereas continual means occurring repeatedly at intervals over a time span:

I continually lose at poker.

I should also mention that continual is often substituted for continuous, and would be correct in most contexts, however the converse is not generally true. That is to say,

The water flowed continually over the dam.

is okay, but you would (hopefully) not mean

I continuously lose at poker.

since that would imply that all you do all day long is play poker and lose.

It's quite true that both level and standard can be regarded as synonymous. However, there is indeed a subtle difference between them.
Suppose there is a competition where there are ten levels (ten rounds; you can participate in a round only if you qualify in the preceding one). Now, there can be different players in each level. However, the standard of the players in each level differ. Agree? As in, the quality of players in each level are different. In level 8, there can be player who has just luckily cleared the seventh level. Also, there can be another player who plays extraordinarily well. This means, the standard of this player is way better than the former.
So this is where the difference between level and standard lies.
However, based on context, you can use either of them for the same purpose.

As regards to you being rejected from job, I think your boss just wanted to tell you that you don't write good English (according to him). Simple.