It’s a lazy joke that the other person already made better.

The sarcasm/joke is obvious, it just wasn’t funny.

There is absolutely no way to determine if somebody is being facetious or serious over the Internet without further context. (Use a damn /s ffs)

Sorry, I should have tagged it properly.

Warning! Sarcasm ahead.

<sarcasm>Ahem, it’s the Gulf of America. Please get your facts right</sarcasm>

Edit: Jerboa eating me tags. Let us try it this way:

<sarcasm>Ahem, it’s the Gulf of America. Please get your facts right</sarcasm>