Perhaps From my knowledge an enderman spawned and maybe was attacked by water you probably took off Weather And from what i know it probably died from that rain and you didn't notice and Quick Teleportation when Enderman's take water is normal and you probably made direct contact so it was trying to avoid rain and attack you so teleported back and fourth avoiding rain and attacking you at the same time with you not noticing that rain was probably off for you but somehow enderman's take the effect still and eventually died
And Since you said it died more mobs spawned probably because.
There's a maxium number of monsters on xbox so it probably ran out of space then when the enderman died
Mobs had a chance to spawn since.
Endermans do the most damage in Minecraft. of all mobs in the OverWorld Except preety much Creepers.
Physically Endermans are the strongest mobs in the overWorld.
So they're spawning Rate is Less then other mobs since skeletons aren't as strong same to zombies.
And creepers are good damage but easy to defeat so they're spawning rate's Higher then Endermen.
Now I tested all these facts so this should be the issue test you're minecraft weather next time and you're problem should end.
But if this doesn't solve the problem i don't understand why it should do that
And sometimes minecraft weather bugs out causing it to rain without u see'ing the rain urself but still effecting mobs which i experienced for myself.
On any other Perspectives i don't understand anything that would cause this misunderstanding.
If This Continue's Reply To Me And I'll See If I Can Explain A Reasonable Example To Help You