This is a great response that captured my feelings well. I'm not sure why the replier assumed the ex was initially angry, to me it just sounds like they were telling a story about something that happened to them that day. If I was describing this to a partner and they assumed it was traumatic for me, I would be perhaps a bit flattered by the concern, but mostly just confused. Because that is a significant overreaction to a common experience.

A professional mechanic is going to know much more about taking care of cars than us, that's what we pay them for. And it's normal (and thoughtful) for them to give people advice that we may need to look into more later on. And if the partner kept thinking I would internalize feelings of inadequacy from these mundane experiences even after I corrected them, it would be both annoying and insulting. If anything, that would be patronizing.

Also, if I told a story where I described not knowing something that would be useful in the future, and my partner did know about it, I would want them to offer to teach me about it. Accusing your partner of being manipulative just because they try to help you with a problem is both cynical and immature. I pity people who are so jaded as to see genuine offers of help as instead malicious, but I would encourage them to at least try to assume others are engaging in good faith until being given a reason to suspect otherwise.