It is pure P2P, the nodes do not help in holepunching but to discover first few peers, a node is just a known peer. Anyone can become a node.
You need to look into Kademliya algorithem to understand how it all works.
Discussion
I think you might be too dumb to continue this conversation, but holepunching requires a third party by definition so Ill leave it up to you to tell me who does it in this case
Perhaps you are too smart to understand, but I will try:
Unlike traditional and common holepunching methods, there is no requirement of a third party STUN server in Kademliya.
The peers themselves act as a stun themselves(kind of) and help in holepunching.