Hello and welcome. I would advise reading the stickies on this forum about husbandry. Whoever told you that you wouldn't need a humidity gauge steered you in the wrong direction. Let me guess, big box pet store employee? My guess is you have husbandry issues, but vomiting could be more serious than just that.

I'm guessing since the vet identified it as vomit and not a regurgitation that there may be an underlying issue. There could be several fairly easy to identify reasons for a regurge, but vomiting often requires a vet visit, to a qualified exotics vet.

If it was a regurgitation, it could be a husbandry or stress issue, or possibly spoiled prey. But my advise would be to bring the snake to a qualified vet and go from there.

Regardless, you'll probably want smaller prey for the next few meals. Regurgitation and vomiting can really be detrimental to the snakes insides and smaller prey will be easier to swallow and digest.