Product Manager thinking like an Engineer

I have one PM in my team that is previously a software engineer. He's new to product management and knows the basics, but I noticed that he tends to look at things 'like an engineer', meaning he analyses the solution first as an engineer and then would just declare it is 'not feasible' just because. He would sometimes get into heated arguments with the dev team, and it usually ends with 'if you know so much why don't you code it yourself?'

As an ex-engineer, I see his POV but I do think he needs to shift his way of thinking. How would you approach this? I had a 1:1 with him and brought it up, and I would assist him every now and then.

Edit: Massive thanks to everyone who shared their thoughts! I decided to give him another chance since I really think he's gonna be a good PM. I did talk to him again and told him everything straight to the point.