In the tera incognita challenge, the science civ(Joseon) doesn’t have the same science stars requirement as the other civ.

It's the only civ with this behaviour.

Science Affinity cultures, oddly, have a higher threshold for getting science stars than other cultures.  I'm not sure, but I think they're the only affinity with a boosted requirement.  This was added a long time ago and was meant to counterbalance the strength of "Collective Minds".  Now that that affinity bonus has been nerfed, maybe the requirements for the stars can return to normal.

That was also my assumption, but on a regular game it doesn't behave like that. ( at least in the ancient era,)