The reason people say stuff like that is that they don't want to put themselves out on a limb. With the odds, its much safer to say "This guy is not NFL material or will make it...." vs saying the player has a chance. Then when it happens that the player doesn't make it, they can always say they knew it or nailed it feeling smart.
There are many factors to why a QB will make it, not just arm strength or the ability to make certain or the majority of throws, I.E. End zone corner route, back shoulder, short screen to RB or TE, rocket slant, etc..
Many novice individuals just think of passes as a general but don't really understand a QB making "ALL" the throws which is like a bunch of tools in a toolbox. Need the correct tool for the job. They don't understand reading defenses or reads. They don't understand correct footwork. They don't understand there is a certain accepted threshold for the size of a NFL QB's hands. My point is they don't understand all the stuff that makes a good or great NFL QB. They just like to make blanket statements then let you know they were right. "See, I told ya....".
If you want to know how much he really understands, ask him what CJ is lacking in his game or the reason(s) he won't or wouldn't make a good NFL QB. If he can't come up with sensible reasons, then you can summarize that your friend really doesn't know shit.