If the average pace evened out to mile pace then wouldn't this be training the same energy system(s) that all mile pace sessions develop? This appears to be an aerobic session that generates a high level of lactic acid, which in turn develop lactic enzyme production and condition specifically for aerobic efforts. I believe Canova would refer to a session like this as aerobic power, but I am not entirely sure. Also its worth noting that this session was probably done a tad bit faster than mile pace, as you should be able to do 20x200m @mile pace with 30 seconds rest.
This session is definitely not anaerobic, running mile pace with short rest is almost entirely aerobic. Anaerobic efforts rely on non oxygen dependent systems.