What does "play the trumpet" mean?

It is a euphemism for fart, as in Dante’s Inferno, last line of Canto XXI:

ed elli avea del cul fatto trombetta.

And he had made a trumpet of his ass. (trans. John Ciardi)

Quite simple,

you're right, this IS NOT any sort of standard idiom in English.

Please read this detailed answer, on the same topic: https://english.stackexchange.com/a/197637/8286

If the above three sentences aren't clear enough: in the title the OP asks "What does “play the trumpet” mean?" In fact, quite simply, the question is unfounded: it means nothing, as the section from the post in question is an incoherent "attempt at" using a "cheeky idiom": a meaningless sound-collection, assembled from fragments of phrases the writer has heard.

It's a case of "it's just that simple."

As is said over and over and over and over and over on this site when this (common) issue arises, it's literally just the syntactic equivalent of a typo: a "type phrase" if you will.

Note once again that, indeed, this is a commonplace, topical, problem in English professional writing today (not to mention the scribblings of incoherent illiterates on the internet).