Don't doubt yourself. You're commenting on hackernews without verifying that the "COBOL defaults to random date in 1875" thing is true. A 12 second google search for use of the word "COBOL" with this 1875 date from before the viral tweet doesn't turn up any results, ChatGPT et al don't know about this COBOL default date thing, having a datetype that defaults to a random date in 1875 wouldn't make any sense, nobody has linked to any documentation supporting this claim, there's no reason to believe it etc.

I think you have exactly what it takes to uncritically accept whatever you see at first glance and comment about it on social media. You're doing it right now!