I'll bet theres a real topic of conversation there , talking about e=mc2
Hey go....Enjoy his company expect "nothing" but if he makes a move just have your mind made up already
I don't think many professors ask students or former students out to dinner just to be friends. If anything, they would avoid actively pursuing any sort of relationship because of the teacher/student factor.
Can't say for sure, but he probably has an interest in you.
Do it!!! Enjoy!