by definition it is "a place where a river or other body of water is shallow enough to be crossed by wading." So naturally he would be crossing here.
Of course, another etymology of place name comes from here - Peniel, though that is a place that has other etymologies (as I covered in earlier years).
This is an example of a non-explicit etymology, as the text does not attribute the name to this incident. But non-explicit etymology happens elsewhere.
There are other options. This could be the name of the place, for other reasons, and what he did there was called that after the place. Or, because of the name of the place, what he did -- wrestling, or whatever -- could have been called by some other term, but for poetic purpose a word was selected which echoed the name of the place.
Shadal cites Gesenius:
וגזניוס אומר בי אמר כאן "ויאבק" ע"ש הנחל יבוק