Yes, I think Patricia is correct. That is what I was going to suggest.
If you have two shops, and link to your other shop this could also be the case. (I have two shops, so I know this is part of the traffic).
Mostly, it's probably from the suggestions that come up at the bottom when you are shopping and click on an item, other "items you might also like" from other shops come up. Do a search yourself and pretend to be a buyer and see what we are talking about. :)