Background story: Friend from uni managed to convinced me to go eat (which I haven't done a lot recently). Arrived at the place, no table. What do you think Pascal would do ? Spot a table of four seats occupied by two people, put up his most irresistible face and go ask for permission to share their table. Once sat down my friend (incidentally, religious type) called me "wierd". We then talked about other things, but once in the tube, later on, I wrote the following email to my friend...
Some people think that other people, other humans, are good unless proven otherwise. (In standard conditions of course, something like the educated environment of London, not war zones.)
Some people think that other people are bad unless proven otherwise.
Those two point of views can be debated philosophically. Some religions decided to have a dogmatic point of view on the question and shove it in people's minds. Some cultural environments promote one point of view other the other one. And usually parents brainwash their children into believing one or the other.
As much as I enjoy the philosophical discussion for its own sake, I usually let experimental results drive my beliefs about reality. And my experimental results are: of all the years I have been alive, 99% of the people I met and asked a favour to, were nice enough to give it to me. Maybe some other people, with a different personality, a different look and a different way of talking than me have other results, but in my case that's what I have observed. Consequently when I am looking for a table in a busy fast food restaurant, asking for a place, is not weird (as you called me) but the logical thing to do.
I know that some people would not have asked because they would feel any refusal as shameful. I don't understand shame. So, yes, there was a small chance that the girls would have said no, if we think about it, for a reason as trivial as because they might have been waiting for friends to come. But as I said above, when I know that something which has a beneficial outcome has a small chance to fail and a big chance to succeed, the logical thing to do is to try. The only good reason in my book not to do something is a high probability to fail :-) ( unless that thing is really, really important )
Also, humans (at least the people I have always been with) like helping each other. I am sure that those girls were actually happy to help us sit. The way they looked as us when we left (I said "thanks" to them, but you didn't) tells me that they actually enjoyed our company. It's human to want to help, it is an evolutionary selected mental trait, which disappears only in exceptional circumstances.