That video wasn't of the national guard it was clearly police of some kind based on the uniforms. Also typically the national guard units they activate for stuff like this are often the MP units so they would be trained on law enforcement specific things. Either way it doesn't excuse or justify that blatant misconduct in the video.
I'm a member of the national guard and I, along with many of my friends, did not sign up to be police officers. That said, in Minnesota they called up every unit it seems. I'd understand civilians to easily confuse police with the military particularly after seeing a Humvee drive by, but if you take a closer look its easy to distinguish.
Also note, we take orders directly from the governor of the state, not the police, nor the president of the US unless activated.
The other thing to think about is, if they activated the entire MN guard, many of these folks are not military police or have received any kind of light MP training. Typically the guard is there to just provide assistance. If they end up doing heavy-duty police work or real riot control, this is how we end up with a kent state type situation--most guardsmen have civilian jobs, so imagine one day your working your IT job, the next day your expected to be a police officer.
The National Guard is effectively the militia of each state. They report to each governor first, and if activated, report to the US military. A traditional guardsman has a civilian job, 9-5 M-F, then one weekend a month 'drills' as a part of the unit. You can get activated, at which point your civilian job has to let you go serve. Most common activations are for statewide disasters--tornados, floods, hurricanes--but most recently medical units were deployed for covid relief. National callups would be to help the us military in Iraq etc., but at all times the guard serves the state first.