I'm glad you ended up having a working relationship with your mechanic but I don't think it's really relevant here. Your mechanic is not maintaining an open source project. He's fixing your car. Which is a great solo project.
I think you're confused about my perspective so let me be clear: I'm not concerned with "defending" the reader from "meanness". I'm suggesting that investing in any project run by a single person is risky: more than likely if that person quits then the project is dead. That's strike one. The fact that the single author has a history of being combative with open source collaborators suggests it might be harder for the project to ever move beyond being a solo project. That's strike two.
All of this is just common sense. I'm sorry if it rubs you the wrong way. If your mechanic decides to stop maintaining your car in the future there will be hundreds of other mechanics waiting to take the job (and, importantly, your money). A solo open source project depending on volunteers is a lot less likely to have that.