How do you talk with someone who laughs after he makes a normal comment?

I was in a meeting and noticed one of the attendees, an adult in his 40s, laughed after everything he said. The comments were not funny nor was humor implied or appropriate.
Usually if someone tells a joke or makes a humorous statement I’ll smile or laugh along even if I’ve heard it a dozen times. But this seems different. Can it be a nervous tic?
I watched the rest of the group, a stodgy group of older PhDs, and no one else laughed or even smiled. That seemed a bit rude to me. I want the guy to feel comfortable but the laughing is just plain weird.
Should I smile or do a short forced low level chuckle – like one does when hearing a “knock knock” joke from a 5 year old nephew? Do I just ignore it an move on without cracking a smile?
What would you do?