Passive mobs are spawning with a low light level

Passive mobs don't require a light level in order to spawn (as far as I'm aware). This is only in place for hostile mobs

This is what made me think that passive mobs should not spawn during night time

That is an unofficial and community made wiki. It is not going to have correct information.

I'm sorry, I'll try to get correct information next time

Did you see them spawn there or did you just generate these chunks?

These are newly generated chunks 

While it's true that passive mobs don't spawn in dark levels normally, this restriction does not exist when the world is initially generated and populated with mobs.