It's not their responsibility to teach but it's also not my responsibility to keep abreast of all social developments. It's inappropriate to gatekeep due to someone's naive ignorance.
Picture this. Sitting at a table game and someone drops a term or phrase that I don't recognise. Am I going to run to the toilet and google that term? Or am I just gonna say 'yo, what's that mean?"
How on earth did you stumble across a comment that is 5 days old?
No objection with your framing. In fact, I tend to agree. My disagreement was the narrow / binary lens applied by the previous commentor. Their perspective ('your responsibility to learn') is/was an extremely dismissive approach.