Hi Dominique glad you're enjoying the lessons!

Overall, I'd say this song is in the key of D minor. That said, he does use D Dorian in that first solo.

You could also think of the scale used as C major, or A minor - all of which contain the same notes. But since the tonal center of the passage is D, it would be most correct to think D Dorian in that section.

Hope this helps!

Mike