It’s been a while so bits of this might be wrong. Manifolds give me PTSD.
A euclidean space is one where pythagoras’ theorem is true, like on a piece of paper. Even if you roll up the paper, everything still works the same. The angles of a triangle still add to 180 etc
But the surface of a sphere doesn’t work like that. You can’t fold up the paper into a sphere, it’s fundamentally different. Geometry changes a bit on the surface too, and you have to modify pythagoras theorem for it to describe triangles in one of these spaces. And the internal angles don’t add to 180 anymore.
These are non-euclidean spaces, aka Riemannian spaces.
So the meme is saying “ha ha you’re in a non-Euclidean space, it just looks like that because you’re small, dumb dumb! Why don’t you draw a big triangle, measure the angles and then cry yourself to sleep?”
Ah thanks! This is why I have manifold PTSD but also that was genuinely helpful.
This was covered fully in the only course I failed in my physics masters, lol.