Hey Tim!
I’m actually playing harmonics on both the E and A strings (open) on the 7th fret – the sound you’re hearing is just both of them together 😅
I call it a ‘harmonic strum’ and use it a lot in my playing where I will quickly sweep the harmonics rather than pluck one at a time.
It’s a horribly difficult technique and took me many many months of failure to see if it was even possible, but it is!
Hope that helps 😊