Rapid XP accumulation in Zwift Run

If I join the slowest May Field pace partner and quit after the ten second timer elapses, I get a substantial XP bonus (about 1/4 of the way from level 5 to 6) even though I traveled no distance. I did this successfully three times in a row because I couldn’t believe it and jumped a full level. If it matters, I had completed a ‘real’ 2.5km run just prior. I’m guessing I could have maxed my level in 20min or so