Yes it could still have come from the plants you purchased. They could have had eggs on them then hatched after you put them into your tank. I have even had a hitchhiker come from fish I purchased. I found a baby snail in a tank that had no snails or live plants....go figure. The best I could figure on that one is that it was in the bag with a fish I bought and it was just so tiny that I didnt notice it. I only had one(that I know of) I have 7 loaches, all of which are more than happy to use snails as a snackie. You probably have alot more snails in that tank that you just havent seen yet. Take a looksie at the gravel and around the plants...you just might find some more yet.
