A320 wingspan = 34m (half = 17m) | A320 main gear span = 7.6m (half = 3.8m) | 17m - 3.8m = 13.2m = Right wings prortusion from the centre of the right gear.
Sirus SR22 wingspan = 11.7m (half = 5.85m)
Width required for the SR22 NOT to go under the A320 wing = 19.05m
Measured on GoogleMaps the width of the taxiway from the centreline to the edge of the surface is worse case 13m, best case 17m, although based on the video and signage I would highly suspect its closer to the 13m point. So with some facts, we can be fairly certain that the SR22 did go under the A320s wing one way or the other, by how much, that depends on the exact position.
More importantly why does the clearance of anything matter in the slightest? Just because ATC clear you to do something, doesn't absolve you from all responsibility. Has everyone on this forum ALWAYS landed when you are cleared to land? No...you've gone around as well. If ATC has cleared you to taxi somewhere and there's an A320 with the ground crew where you were not expecting them to be, you stop behind and ask. You don't try and squeeze UNDER the aircraft. The cause may have been a miscommunication or poor clearance, however, there is very little excuse for poor airmanship.