Does anyone know what they're smoking in that big pipe at about 25:15 into the video?

Imagine showing up in a remote village as an anthropologist and after a few hours the first thing the villagers ask you to partake in is the equivalent of a huge bong hit. And you don't want to offend anyone by refusing...

Actually your comment reminds me of this guy who travels to Vanuatu to try really strong kava. The village chief invites him to drink multiple bowls, which he can't refuse: https://www.youtube.com/watch?v=-BtP_B4TBWs

Probably tobacco. The article mentions it was introduced to PNG in the last few hundred years, and the plant made its way into the highland tribes despite limited travel and trade.