I feel guilty..

I went to a restaurant that my friends friend worked at. My friend’s friend was our server. The server and I hit it off after our friend left. I asked for the check and a different person brought the check out. There were two beers not on the check. I assumed they must have been discounted off. So I paid and left over 20% tip. But then as I got home I thought what if was a mistake? I couldnt find him at the time/ I assume the person who brought the tab out was asked to by him cuz he was busy right? So they would just bring me whatever he put in the computer, right?