Deep drifter on surface?

[Lithembia]

I had a drifter groaning outside the door and when his head clipped in thought it looked different, and then when I killed him in the morning it was a deep drifter. There aren't any holes nearby he could have crawled out of (there is one but it is on the opposite side of a fence), so how is he on the surface? It is very low right on the shore of a big lake but shouldn't surface be Y level 1 regardless of its height above the mantle? 

[LadyWYT]

1 hour ago, Lithembia said:

There aren't any holes nearby he could have crawled out of (there is one but it is on the opposite side of a fence), so how is he on the surface?

I can't recall having ever seen one crawl out of a hole; while they can spawn somewhat close to the surface it's still a bit too deep for them to really wander out of caves and into broad daylight. Are there any mineshafts nearby? Drifters can climb ladders, so if there is a shaft somewhere nearby then it most likely crawled up the ladder. Likewise, if you have underground portions of your base with easy access to the surface(ie, no doors, open doors, etc) then it's possible there is a dark corner for them to spawn in there before crawling out.

If a temporal storm rolled through during the night then the drifter was most likely a leftover spawn from the storm. In that case, the drifter should appear to flicker in and out of existence. If there was rift activity at the time of the storm and it spawned from a rift then it might not be flickering, but I'm not sure if rifts that are active during storms will produce stronger monsters or not.

The only other thing I can think of currently is that if you are using mods, it's possible that a mod may be causing some unintended behavior.

[Lithembia]

I don't have any mineshafts there, though thanks for the terrifying warning about them taking the ladder. I usually put ladders every other block and they seem to get stuck on them but I'll be sure to keep an eye out below. 

It wasn't a temporal storm. There is one of those dropoff caves on the other side of a fence from it, and farther away another cave entrance on the same side of the fence. Right now I'm going with it spawned in the tunnel and hiked out and over to my house? 

I have a couple mods but nothing changing spawns, just the better firepit and one that makes farmland drop blocks with nutrients included. 

[Maelstrom]

I've had drifters hike a fair distance from a cave.   I believe spawn distance is about 65 block radius.  I'd put my money on a natural spawn and he wandered on over to say, "Hi"