Is it normal my ex seems fixated on my friend?

I'll keep this as short as possible. My ex and I have been friends for a few months now. Soon after we started hanging out again he suddenly brought up my friend, he said "I see your one friend has a boyfriend now." I asked why he mentioned it. He said "don't get jealous. I'm not interested in her or anybody." So I forgot about it. Just recently he followed her on Instagram after I tagged her in a post, likes her pictures constantly and wrote a suggestive comment on one of them. When we were still together he made inappropriate jokes about her, like "she's coming over tonight and you have to sleep on the couch." This doesn't make me nearly as jealous or sick with anxiety as it would have when we were together, or even during the no contact period after we broke up. I just think it's a little weird since we dated for over a year and she's one of my best friends. She may or may not have stolen from me when she was on drugs, I still don't know for sure, but it's in the past. Not sure how I feel.