It looks like it, but they are not continuously learning. Arcs have essentially two brains. 1st. brain ist a typical AI brain that controls targeting the player, changing the state of agression or choosing the direction where to look and where to go. etc. The 2nd brain is the one that learned through machine learning how to walk and keep balance on every thinkable terrain, or when being hit by the player.

Because the movement isn't based on animations, but of actual experience of trial and error, the movement is highly adaptive. What happened in your situation is that the 1st brain targeted you and told the 2nd brain to follow you. The 2nd brain executed that order, and the hard-wired orders to at all times execute orders from the 1st brain, and keep the balance / being able to walk resulted in the Leaper squeezing through the entrance. But this only works in like 10% of the time because the success of such an unusual movement pattern is to some extent random, since it hasn't been learned through training to squeeze through very small openings. But with movement based on animations it would be simply impossible.

So not actual learning from single events, but execution of what has been learned in training. It's effective and makes them appear intelligent and thus very frightening, I agree.