Going to the actual source (article published by Pro Football Focus, of which the OP's link is a derivative article by Patrick Brown), here's what they said:
Nothing in there indicates that the folks at PFF gauged Hooker against the other QBs on the roster. So no way of knowing if they know anything. Either by analysis, or by having an inside source on the coaching staff.
And Patrick Brown, the fella who wrote the derivative article that got linked first, he didn't add any analysis or hints of inside sources, either.
Without any of that, their guess of Hooker is roughly as well-founded as yours or mine, I'd say.