Uber-jackal effect even for monsters I didn't kill?

So I'm hanging out on the last layer in the fungal caves with the pool still active and decide to try setting up an alarm trap to try and farm mushrooms.

Everything seems to be working well and the fungoids are killing each other without me lifting a finger. My mushroom stockpile grows.

However, I soon notice that the occasional fungoid that breaks off of the pack and comes after me is much tougher than when I started. MUCH tougher. I check my kill list and have only killed ~20 fungoids of each type.

So I start watching them more closely and, sure enough, I see their experience rating go from moderate to highly experienced without me ever killing a single one.

I thought the uber-jackal effect was only a problem if I killed the monsters myself. Does it also apply if the monsters are killed by any means or maybe even just generated?

Maybe this is a bug?

Thanks and please let me know your thoughts,
blargfoot

From what I have seen, my impression is that fungoids spawned by the pool are a special case. They seem to grow stronger (or more experienced) very quickly, regardless of how many of them you killed. I don't think this is the überjackal effect you are seeing.

By the way, I once had an altar nearby the fungoid pool, that was pretty awesome. It allowed me to exploit the mechanic for lots of piety - although it was still dangerous, because of the paralyzing rays.

Isn't this the case of one monster killing like 10-20 of their brethren and simply gaining levels and becoming more powerful?
I know this is what you can do in the bug temple as a bard - tame a bug, make it kill other bugs, then eventually you get a superbug that can pretty much kill anything.

I've seen exactly the same, I got an alarm trap right beside the pool and then build a short corridor of doors (the fungoids don't appear to open or smash locked doors). Then I waited at the end of the corridor intending to finish off the ones that got through. The ones emerging from the pool were definitely increasing in experience.
I don't think they ever learned to see invisible though.