Yes, I think professional criminals if it is a kidnapping/ransom scenario, and that's primarily because despite the digital investigative prowess of the FBI it doesn't seem to have the aptitude or ability to track and trace the digital footprint of whomever did this. We have to think - this case reached the President of the United States, who then unleashed an army of resources to locate the perpetrator(s) and Nancy. This means that the FBI probably isn't the only government agency involved. I'm sure they've looked at whatever satellite data they have from the area, and I'm sure the NSA and similar agencies have tried to decode the digital footprint of the sender of those emails. And all to no avail. That implies a high degree of sophistication, someone who has done this before, and somewhere else on the planet.
Everyone saying the guy in the video looks amateur is doing so by their own "algorithm" or confirmation bias, IMO. This guy knew exactly what he was doing, and the earlier date video reinforces the notion of high sophistication in planning. He knew all of the 'actors, factors, and risks' well in advance. Guy is altering his gait walking up to the door. Guy clearly doesn't really care that he's on camera. I think he just didn't want anyone to see Nancy on camera.
An outlier is that there's a possibility that there is something under the surface that could've put this plan into motion, with a motive perhaps being to enact some sort of proxy extrajudicial justice on SG. "A threat carried out" in other words.
Could also be a crazed fan, but I just think that'd be too easy to decipher and an arrest already made.