He is openly blaming Van Gaal for not listening to him back then, he scoted both players and it was obvious to him that they do look like "United players" but the staff didn't listen to him.

@Golazo I dunno, its sure is easy to say that now that they emerged. To be fair, it wouldn't have been too good for M'bappe to join United, wouldn't have been good for his progress back then.

@Emo he is unstoppable as long as someone gives him a chance, if Rashford got his chance I guess Mbappe would probe himself on training so...idk

This was around 2014/15 Mbappe was still developing and its hard to sy if he would have been just as good had he moved to United. Monaco was essential to him becoming the beast he is today.
United also had too many players in that department. Martial was the big investment at the time and Rashford was coming through the academy. He's been great so far. Just not as spectacular as Kylian.

A force like Mbappe is unstoppable and he would get a chance anywhere, thats how good he is, a talent that you can't ignore.

And we are talking about Manchester United, a club that did give a chance to many young players that ended up becoming legends.

@Golazo Well, he would have propably suceeded but maybe it would have been harder for him because he would have needed to adapt and deal with more pressure, there is also the risk he would have been injured (a lot easier to be injured in PL).

Manchester United will always cater to an academy prospect over buying someone young in the same position. That's very much who the club is, and the self-belief they have that they can bring players through. Whenever you see United buy someone young (e.g. Martial or Shaw) it's because there is no one in the U-21s at that position that is particularly impressive. As soon as Martial was purchased as Rashford burst onto the scene, United was never going to buy another young striker. Giggs knows this.

Well that's not really always the case or lets say that at least it's not that abnormal to not have a player that can be good enough for the first team from the academy.
That doesn't mean that they wouldn't buy a great scouted youngster player, even Giggs as a local boy that lived in Manchester since he was 6 trained for Man City for a little bit but always wanted to join United and so he did, so it's not that unusual to sign good youngsters, even with signing Depay and Martial and giving chance to someone like Januzaj it's not like they wouldn't normally sign a great youngster because they could but they didn't agree, I mean if it wasn't to be the clubs policy they wouldn't have scouted those players in the first place.

I believe Giggs is not lying to anyone as he did sign his first contract at round 16 years old which would have kinda been Mbappes age at the time he got scouted by United so it was a mistake not to listen to him but Van Gaal and Giggs didn't get along in some areas so this is not a coincidence.