I have never heard a coach say this. OP stated their S made a verbal commitment with the CalTech coach (commitment = coach support in admissions for a spot on the soccer team; it doesn’t matter what round of admissions that support is for when assessing the validity of said commitment). Sure, some break those verbal commitments because they don’t see any issue with that.
We can hypothesize all day what may or may not happen if OP’s S continues looking (which they’ve already said he wasn’t going to do).
As always, I defer to those directly involved in any situation. OP’s S should ask the CalTech coach if he can continue recruiting…the answer to that question is the only one that matters. Of course, I would not recommend anyone ask that question.