Why is my site getting error reports from users with iOS7 on a MacBook?
Ruling out a possible hack to get iOS to run on a MacBook natively (which would get a lot of publicity), I can see the following options


Users didn't know enough about their system and just picked the things most likely (which means that you could have error reports from users with OS X 10.7 on a MacBook as well as from some with iOS7 on an iDevice mixed together)
One or the other is just the default option when filling in a bug report on wherever you are getting them from and people are lazy
Users have been accessing your site via the iOS simulator on OS X. Possible but rather unlikely (unless you have a very special site :-)