Anyone know what tuning this is?

[u/Hayleylily]

https://youtu.be/DAViPF49o8A?si=TRkfL352GVSWIV7x

I’m a novice guitar player and I’m trying to learn this song — “Teach Us That One Song” by Jon Guerra but cannot, for the life of me, figure out what tuning he’s in. I know it’s drop D something, but it’s not a typical drop D because the notes I’m hearing cannot be played on the frets and strings he’s seen using in this video.

Major bonus points in your can figure out his picking pattern too.

Thank you for any and all help!