Conspiracy is merely a secret plan made by a group of people to accomplish an illegal or immoral goal. Conspiracy happens all the time, and it often involves big, sophisticated businesses or political interests. That doesn't mean that conspiracy abounds in every event. I think Oswald acted alone. There was a moon landing. New Coke was a poor attempt to modernize a product people loved.
On the other hand, the Enron scandal resulted from conspiracy as have other events instigated by big business interests one would have thought would have seen the danger and the likely outcome. Often conspiracy has been proven. Tinfoil hates aren't required. Greed is an extreme motivator.
Sport hasn't been immune to conspiracy, and not all "conspiracy" is organized or results from a written memo or verbal instruction. Often mid-level players know what actions are desired by those above them and respond to such desire in what effectively functions as if it were an organized conspiracy.
I don't know whether on-field officials place a thumb on the scale. I doubt seriously they have received explicit instructions to do so. Have they ascertained such desire from the league and acted more or less independently to implement? I don't know, but I don't see how such a scenario can be ruled out. It happens in many big business scenarios. Why should the NFL be exempt?
I do think the NFL has set itself up for a future scandal, and I don't think it requires tinfoil to hold this view. The rules have become so interpretive that it would not be difficult for an official or officials to "interpret" a play or plays in a manner to influence the point spread or the over/under.
The NFL once eschewed full-time officials because many of the best worked in professions they were unlikely to leave. Every year some of those veteran officials retire. Younger officials arguably could be more vulnerable to temptation. But we shall see.
In any case, the NFL is big business and can become tainted as easily as any such entity. Gambling interests make such an event more likely. I do not understand why anyone finds this in any way unbelievable or unlikely. The ticking time bomb is always a few foolish decisions from being activated.