That is just another media talking point.
No college QB is truly Pro-ready. They have an entire new offense to learn, and the NFL game is so different than the college game no matter what O a QB came from in college.
I admit that there are some exceptions to the rule (to a point) especially with college QBs that come from homes where Dad was a Pro QB (Luck, Manning) and so they have more mental preparation than most. And they can thrive more quickly.
But the even bigger difference between college and Pro's is in the D's the QB will face. The D players are bigger, better, faster and the DCs devise so many schemes and ways to disguise what they're doing.
Sure, some come out with more maturity, have played more (taken more snaps, played more games, etc.), have better mechanics, have better leadership qualities, etc.
So in that sense, Goff was more Pro-ready than some others, such as Wentz. But being ready to be a Pro, versus being ready to lead the offense to scoring points, is quite another issue.
Some teams have good enough QBs already on the squad to allow the new kid more time to develop. Others do not. Tampa, for instance, had a hole at QB and Winston was "Pro ready" enough to be go in and be as good as or even better than anyone they had.
The Rams seem to have a good enough QB in Keenum that Goff is going to have the luxury of developing more before he's thrown to the wolves.
I think that's a good thing. It doesn't mean the Rams made a mistake with Goff. But......only time will tell. Right now it's all speculation.