Dad could preferably have talked about the dangers about talking to strangers online and checked the chat logs together rather than checking it like that. But I see what drove his actions.
I had this with my mother. She would check up who I talked to and randomly check on my chats. I hated it because I wanted my privacy however some adults did talk to me. It ruined my ability to trust her once I turned 18 along with many other things.
That's what I was going to suggest. I have my dad and he's the one I trust in the whole world. As full grown adult, I tell him who I talk to and let him say hello on voice call with my online friends. I've been using the internet for over 20 years aka since I was in Elementary school. With my mother, I felt forced to give her my passwords and didn't want to tell her anything once I became an adult while my dad I told him everything because we trust each other.
He's not a bad dad but there are better ways in doing this