The terminology around AI (AI, ML, DL, RL) is a bit confused sometimes. You’re correct that deep reinforcement learning does indeed use deep neural nets, so it could be considered a part of deep learning. However, colloquially deep learning is often taken to mean the parts that aren’t RL (so supervised, unsupervised, and self-supervised deep learning). RL is pretty qualitatively different from those in the way it is trained, so it makes sense that there would be a different term, but it can create confusion.
The terminology around AI (AI, ML, DL, RL) is a bit confused sometimes. You’re correct that deep reinforcement learning does indeed use deep neural nets, so it could be considered a part of deep learning. However, colloquially deep learning is often taken to mean the parts that aren’t RL (so supervised, unsupervised, and self-supervised deep learning). RL is pretty qualitatively different from those in the way it is trained, so it makes sense that there would be a different term, but it can create confusion.