You're being too literal. :) I think what she meant it, the theoretical "you" MEANT the note to clearly state "Meet me at McDonalds!" But you perhaps weren't paying attention and maybe you DID just say "Meet me for a burger!" assuming they knew you meant McDonalds because, I dunno, it's closest or you usually go there or whatever. Or...what if you did write "Meet me at McDonalds!" and they went to the wrong one? Or at the wrong time? And so forth.

Now, if you said "Meet me at the McDonalds on Main and MacArthur at noon today for a burger -- my treat -- I've got your number, but call me at (XXX) XXX-XXXX if you have to change plans, okay?" NOW you're communicating. (And obviously I've had to herd people around IRL, can't you tell? ;)