Well, technically it's also most likely a fake tweet... So, it's apparently a double-whammy in that some people think the tweet is real, and that some other people think the Earth is flat.....
It seems to have been around for years..... Apparently it's a faked tweet, for the very purpose of making people think it's real (the maker of the phony tweet thereby getting to laugh at people believing in a false tweet, that's about people falsely believing the Earth is flat)...
Okay, I see that now; there was a tweeted meme version from some time ago... In any case, it's the same basic joke --- and part of the joke is that, although it's fake and created as a joke, many people get caught believing the post/tweet is real... With all such things, we all would be wise to do some cross-referencing before automatically believing almost anything on the internet... Everyone seems to get fooled though, once in a while -- even top-level scientists, govt-type people, corporate leaders, etc... https://twitter.com/flatearthorg/status/730078048503107584?lang=en
for real NASA is a just a front for a HUGE Cover up
the earth was engineered & made by thomas' English muffins
the marianas trench & GIANT OCEAN CAVERNS places close to or OVER 5 MILES DEEP those are all NASA Fakes Cover ups to prevent you from knowing we all live on a GIANT English Muffin.