Sorry, sounds like you might be right … no idea why you wouldn’t want to put a primer down on a new surface like that … bound to be some sort of residue / powder somewhere as it’s dried & for the time it takes to apply a primer, even with a brush, it’s not worth the potential impact of not doing … but if you didn’t provide it, that’s what he might say, but then you did check with him specifically & he said no …
You might want to get someone in to look at it & check, rather than just going off the advice here - there might be an underlying cause that’s nothing to do with the tiling (although that doesn’t sound likely I’m afraid).