Will babies be confused when non-signing babies don’t respond?

This hard to say definitively without asking a baby personally! However, language abilities span more than just signing and non-signing, there are huge variations in communication even just between talkers of the same or similar age, so I doubt very much that it will make much of a difference. Some babies also talk very early too and it doesn’t seem to bother talking babies that other babies don’t talk back to them. Some babies also get taught manners while others end up pushy and bossy, but that doesn’t mean your well behaved baby won’t be able to adjust. In the end babies and toddlers just find a way to carry on, and play regardless of their differences, and that’s pretty much the end of it.