Hey Chris, glad the "learn the notes on the fretboard" exercise is helpful for you. It definitely was for me!

As for that riff I was playing, you've got it exactly!!

The spot you're asking about is just a quick riff using double stops (2 notes at a time). The first strum is an A power chord double stop - 2nd fret of the D and G strings. The next strum is a G power chord double stop - open D and open G strings, but I'm hammering onto the 1st fret of the G string, which then makes the double stop outline an E7 chord (D is the flat 7 of E7, and the G# note is the major 3rd of E7).

I learned that trick from Randy Rhoads. He plays a similar lick (up at the 12th fret) in the live version of Ozzy's "Paranoid".

Keep rocking!!
Mike