Someone who claims to race these cars said that hitting the throttle at caution speeds will cause the tail to swing toward the inside of the track, and that’s exactly what the video shows.
I personally think most of the “outrage” is from people who just want to be part of the mob.
I guess it comes down to how hard the throttle is hit and at what speed the car was going just before. As I have posted before, Sprint Drivers are always hitting the throttle to varying degrees under caution. IMO the cars are not all sliding in the rear under gas. Heck, many will just jump the front end up a little from time to time.