the early party long rest cutscene, where everyone feels sick and Lae'zel wants to kill us because she thinks we're turning. But then we wake up feeling perfectly fine, conclusive evidence that our tadpole is different from normal ceremorphosis.
For what it's worth, that cutscene only triggers if the player used tadpole powers. And I'm fairly sure that the first tadpole-power opportunity (when the game encourages the player to try using it for tutorial purposes) doesn't count. So players wary of the tadpole will miss that important bit of knowledge. Not to mention, players who rest as little as seems prudent given the circumstances will miss other cutscenes, such as Gale saying the ceremorphosis timeline is off.
The game never reassures players who play scared (few long rests, no tadpole usage) yet keeps reinforcing the tadpole's danger. In this way, BG3 punishes player immersion by withholding key information from those who choose to take the threat seriously.
Ah, I didn't realize that there was this condition.
Your 2nd paragraph perfectly summarizes my thoughts on this.