It could be a modern high efficiency furnace that doesn't need to be routed up high.I am a bit shocked a furnace vent wouldn't be routed out your roof or vented to be at least 6" above roof peek for safety.
Furnace exhaust getting in the house (human or animal house) is a potential fatal disaster. It is why furnaces are supposed to be periodically inspected. (yearly is recommended)
Usually those are PVC pipes.
Really hard to say just what is going on here.