Ive read the vast majority of the thread.
I think what happened is this
OP has an unfortunate communication style, not her fault.
Was running late, contrary to many posters, I also feel thats not her fault, people got to wee/be sick/dog needs a wee, that is par for the course, she said she factored that in and probably did but then there was traffic, it happens, no one needs to be leaving hours and hours earlier than need be, so she was late
But,,,, big but, OPs style of communication or that of her partner (who is no doubt similar to her) may well have confused and pissed off the other party
So while they're milling about waiting, going to shops having a milkshake or whatever, they're getting more and more pissed off and wondering if they'll ever turn up and if so, how the afternoon will run as planned, is there going to be enough time, blah blah blah
So while all thats going on, they book another table somewhere so they get dinner nearer home, at somewhere they like a bit better. They leave the other table reservation in place just in case or so that OP wont be left without a table if and when they arrive.
That must be it. Not sure why they didnt communicate this initially. Perhaps they are also very very odd.