This sounds really disconcerting! I'm training to be a psychologist, and we are taught about lots of ways we show people we are attuned to them, but it has to be subtle and somewhat natural. The point is that people do these things naturally anyway.

I do notice my T adjusting her communication to make it similar to mine. For example, when I started using smiley faces in texts, she started using them back. I'm sure she also uses some of my own words and phrases with me that she wouldn't normally use. It doesn't feel obvious though, it just feels attuned.

I vote for telling him you found it strange...