Forget all the stuff out there that says the GDPR protects EU citizens. This is a question of jurisdiction and enforcement. Say I run a blog under a business registered in the US funded by advertisers in the US. A EU citizen that comments on posts issues a GDPR request that I ignore. Their government fines me. I tell them to get bent, I am out of their jurisdiction. What can they do at that point?
If the comment keeps your IP address, and/or your email, or a nickname, it can be considered personal data.
The “simple” rule is : does that info, once used with other data, can allow someone to figure out who you are ? If so, then it’s personal. From there, always validate with a lawyer who is actually properly trained on the GDPR to review your decision.