I’d bring it up, but like you did here. “Son dropped a thing and his first reaction was to be scared of how you’d react. That made me sad to see.” Or something similar.

It can take a long time to make the connection between his childhood and his anger and to begin to see how it can get transmitted to the next generation. If you can help him see it from his son’s perspective and link that to his own feelings of powerlessness as a kid, it might help him see it a little.

I’d try not to come on as judging, but lead with empathy. Especially as he is trying to work on his anger and mental health and has shown improvement. If he is made to feel terrible for one slip up when in fact his overall trajectory has been positive, it may make him feel defeated and less likely to keep working on change.