There are things that you shouldn’t do or say to minors that aren’t illegal, but anyone reading them would still know it’s it’s unethical/wrong/immoral/whatever. They clearly thought he crossed that line, enough that they’d rather fire him and take a chance on losing the court case for damages for breaking the contract. And then they lost that court case.
It clearly wasn’t just “a chat with a minor”. The rumors I’ve heard is that he was attempting to make plans to meet up with them at a convention. That would definitely be in the “big no no” category for a celebrity talking to a minor, even if nothing untoward was suggested in that conversation.
People have been trying to make Blender have some basic CAD functionality, but it’s just not there yet.
I admit I haven’t tried https://www.cadsketcher.com/ with it yet, though.