Six strangers with guns coming to your home and demanding to conduct a search is hardly a friendly visit. And however cordial they are, they have the right to use any violence against you - including lethal - at any moment they decide there's anything suspicious, and the experience suggests even if they are completely wrong worst thing that would happen to them is suspension with pay. As for you, anything you say to them can and will be used against you, and any factually incorrect statements, however trivial and minute the incorrect part is, that you make to them can be grounds to a felony prosecution if they so desire.

So I don't think it can be dismissed as a friendly encounter. I would certainly feel extremely discomforted by such a visit.

The police were polite... so it's not a raid? What if he denied a voluntary search of the house? Would they politely stop investigating them as terrorists and monitoring their internet activity?

Exactly. How it is labeled isn't the important bit here. The fact that they showed up AT ALL based on what appears to be a confluence of Internet searches is what is concerning.

Between assisting the greater good and looking out for number one, they didn't seem to do enough of the later.

IANAL: They took a gamble by letting them in the door without a warrant. That opened themselves up to legal liability, regardless of "nothing to hide" innocence.

If they had found anything that looked suspicious, it would be a different story. They lucked out, this time.

A law school professor and a police investigator teach a class of law students why you can gain nothing by talking to the police: https://youtu.be/6wXkI4t7nuc