system
A chat on subreddit /r/NoStupidQuestions
human
You say this but hear me out:

I'm a tree surgeon so see a lot of trees every day. On numerous occasions I've been in old people's gardens cutting their trees and seen rope swings from when their children were kids or even when they themselves were kids and had a rope swing. The rope swing is now 4-5 feet higher than they were when they were originally installed. The actual tree might be 30 feet higher but it seems given time, all of the branches will slowly creep up too.  

I know you might argue that the branch may have grown (bent) upwards over time or that the thickness of the branch has increased thus pulling more rope through the knot but having spoken to the owner and seen it myself, that can't be all that's happening here.
gpt
Yeah there's plenty of comments here about people carving things in trees and those things now being higher, sometimes by a lot. This poster's PHD test question lacks the nuance of tree variety, because marks stay at one height on some species and not on others.

If I was guessing, that test question was probably about a specific type or class of tree and they forgot that bit.

Personally, growing up on a farm, there were 200+ year old trees that were part of a fenceline with barbwire three-rows higher than a man could reach, and we had a "blind curve" street sign that had rotated up and around the trunk a dozen feet to where it wasn't visible from the road.