Well, I do agree that your husband behavior with the "make out" session was "bad form." I do think the offer to extend a ride to the meeting was an attempt to smooth things over with you.
It is entirely possible that he was caught up in the moment with this other person. Lets face facts, its always nice to be the object of someones interest. However, there is no way to know whether this was an extensive flirtation on his part, or a genuine interest in dating or romance.
Throw him a bone. He screwed up and he knows it.
None of parties know enough about the others, at this point to know where it goes, and if she is willing to meet and discuss there may be an opportunity for all involved to learn and gain from the incident.
On the other hand, if she is unwilling to come to the discussion, then hubby already knows he needs to "throw this one back."