Learn English – Should I use “besides” or “aside from” in the following case

This is an example of elision: a process of omission of words which are to be inferred by the listener. Elision happens in many languages, and follows certain patterns.

For instance, in English, as in many languages, a brief answer is possible, like this:

Q: Where did you go?

A1: To the park. [Subject and verb are elided.]

A2: ? Park. [Possible, but less usual, and creates an abrupt sense. Perhaps the speaker is out of breath, or indicating an emotional state of being disinclined to conversation.]

Q: What did you have for dinner?

A: Pizza. [A one-word answer to a "what" question is not unusual, and not considered abrupt. "Steak" is the direct object of the elided sentence "I had steak for dinner", where there are no prepositions on the word.]

In the sentence:

Nothing the god of biomechanics wouldn't let you in heaven for.

words are elided from the hypothetical sentence "They (= those things that I did) were nothing the god of biomechanics wouldn't let you in heaven for."

By the way, a better preposition in this type of sentence, at least in a more formal setting, would be "into". If there is no complement for the preposition, it is just "in":

Let me { in | *into }.

But with a complement like "building":

Let me { in | into } the building.

Using "in" for "into" is acceptable, but at the cost of contributing to an informal, conversational tone to the sentence (which is obviously appropriate in the context here). This view is probably due to the the bias arising from everyone having had it drilled into their heads in elementary school that "into" should be preferred.

In any case, that would be the only nitpick I could possibly have with the sentence; not its elided subject and verb. :)

This is why is to explains a reason. This is how is to explains a process.

I had three rounds of tough intervews for this job, that is how I got hired. During one of the interview, I nailed a difficult problem, that is why i got hired.

for your example, it should be Speaker B: Is this why you know so much about these topics?