sometimes choices make you
It means that sometimes the choices you make influence who you become as a person.
As noted by @Sam I Am, this is not a normal phrase. It is designed to be the reverse of the first half of the sentence (you make choices), and seems to be ironically implying that while you expect to have control of your decisions, sometimes those decisions can effect (control) you.
In this case, it is also implied that these choices are especially important, hard, or have dramatic (possibly unexpected) results. Less obviously, it is likely implied that some portions of these choices are negative in some way (though this may not always be the case).
Example
During your childhood, you become a delinquent, and end up committing a crime that lands you in prison for 10 years. This choice may "make you" into a fundamentally different person than if you had not gone to prison. Perhaps you now feel compelled to work helping criminals give up their lifestyles (because prison had such a negative effect on your life) rather than if you had not gone to prison and become, say, a wealthy banker.
Alternate Phrasing
Is there any other examples or metaphors that could be meant by that phrase?
The closest I would say would be:
"You (We) are the sum (total) of (all) our experiences"
Meaning what you experience in life shapes your personality, outlook on life and general approach to living.
As Man_From_India says, you have understood is said to have assumed correctly. More generally SUBJ BE said to VERBinfinitive may be paraphrased as people say that SUBJ VERBfinite.
The preposition phrase upon VERBpres.ppl may be paraphrased at the time SUBJ VERBfinite, where SUBJ is the subject of the clause which the preposition phrase modifies:
the people he came in contact with upon reaching land = the people he came in contact with at the time he reached land
You will receive your inheritance upon attaining the age of 21. = You will receive your inheritance at the time you reach the age of 21.
Best Answer
The idiom "What does that buy us?" means, "What do we get from this?" or "What can we actually use these for?" In the context of your example, the person asks what real-world benefit is gained from these academic theories, to refute the suggestion that they have no useful application.
It can be called an American expression because of this country's focus on money, so many think we only care about the financial value of things (and care little for pure academic progress). This may or may not be true, of course, but nevertheless the stereotype exists.
A similar expression is "to get down to dollars and cents" which means to assess the real-world benefit from a particular expense. In your example, you could say: