@KayleneP
By eating her sandwich he did two things.
1) Notice the first few frames. She dropped the filling out of the sandwich due to surprise. So, he replaced the sandwich but had it cut to bite sized pieces so that wouldn't happen again.
2) By eating her sandwich he assumed her bill. This is assumption since it's not explicitly shown. But that probably occurred due to how sit down restaurants work. Since he ate it he would pay for it. That would be how the conversation goes when the waiter comes with the bill. And since he was the one who ordered the rest of the food he would pay for that too.
He didn't say that was his intention because, unless she brought it up, it could be passed off without causing her embarrassment.