"Together or Separate?"

This weekend, while out to dinner with some friends for a birthday I experienced the often occuring case of "couple assumption", Let me explain.

I met up with some friends for dinner at a local restaurant and it just so happened that when I arrived a guy friend of mine was arriving too therefore we sat next to eachother, across from two pairs of couples. Shortly after an other couple arrived and sat next to us. Now my friend and I are purely platonic and there were no bad intentions in our seating arrangements ( besides the vomit inducing view of four googly eyed lovebirds in front of our faces) So, when our checks arrived, it was to my (shocking) surprise that our waitress had put both of our meals on one check. For a moment, I thought, " well, that means free meal for me" but then it hit me. Why is it automatically assumed that one is "together" with another if they happen to be in a crowd of couples? and Furthermore, does that bring out boyfriend/girlfriend behaviors in us to make others assume that??

Ultimately, we both laughed it off justifying the fact that she never asked our party of 12 who was together or separate for the split checks? and as for my free meal? well... all I can say is I left with a full tummy and empty wallet.