Well I think the statement was, haven't seen someone do this much at the line of scrimmage in his 2nd year since manning. It's a little hyperbole, but Romo wasn't comparing him to in his prime Manning, and while Goff is getting help in many different ways by the coaching staff. He is making many decisions and executing at a very high level for a second year qb. Mastered the offense, of course not. Who says that. Understands what he is asked to do and why? Yes. Lets not forget it was reported some play calls had as many as 15 words in it. Lets not forget who was teaching that offense that was harder for the offense to understand then it was for the defenses they were playing against. I think it is totally believable that Goff is making the final decisions at the line of scrimmage.
Agree with one minor exception.
We don't know what is going on in headphone interactions or what the coaching directions are. But I suspect that Goff is both doing what the coaches are asking and adding significant input of his own, whether at the line of scrimmage or on the sidelines or in game preparation.
I would say Goff
has mastered the Rams offense, actually for reasons you state and probably a long list of others if we thought about it more. As you say he is executing the offense at a very high level, I would say for any qb not just a second year guy. He has rarely if at all looked as if he did not totally understand the plays and what he needs to do. And that alone is a formidable accomplishment-- lots of veteran qbs have taken a full year to learn a new offense.
What I think we will see more of going forward is Goff learning to see the whole game in real time on the field-- all the possibilities of a particular play or matchup or defensive formation. There is no doubt a lot of outside the box stuff--say jumping out of the progressions to hit an open receiver or or calling an exotic audible-- that can only come with experience.
Goff is a serious student of the game and has great coaches. He will get "there" sooner than most people think and when he does, look out.