There's video popping up in the Mastodon FB group I'm in, he's indeed onstage with them.
Edit, the group is private so I can't share the vid, but here's some shitty screenshots!
View attachment 40080
View attachment 40081
Just saw a vid of him very, very comfortably playing the solo to "Pain With No Anchor". Dude looks remarkably comfortable onstage and not like he rushed to learn that in any way. Definitely possible he already knew it, dude's a huge Mastodon fan.
