I think a lot of stores promote their registries for various different events, and then people - especially young ones - think those are events where a registry is expected, because it's being advertised, yk?
i find the whole registry thing very alien, anyway. I've never registered, anywhere. When I got married the first time, I compiled a list of what we had and what we didn't, and gave it to my mom. If people asked what we needed, she told them from the list. When I married dh, we only had two weeks from deciding on a wedding date until the actual wedding, so the whole thing was quite informal. People brought gifts based on what they felt were good consumables and/or things that my ex had probably taken with him (lots of linens, a few new frying pans).