Not sure really what to make of this exactly, Keller’s statement isn't an outright dismissal of the abilities of the MLS players, but yet it’s not one of let’s say great confidence in the MLS player either. Basically he just said the American MLS players are athletic and work hard.
Sure, he’s saying all this in reference to Freddie and his previous team, Arsenal. Saying Freddie can’t expect to be playing with Robert Pires, Thierry Henry, or Dennis Bergkamp when he starts his MLS journey with the Seattle Sounders FC.
This is just like how political operatives stir up controversy, by sending a short clip around that takes the question out of the whole context. Perhaps Keller also made some statements about how he thinks the MLS player has a bright future, is getting better, has some skill?
I don't know though, perhaps he was just telling it like it is when compared to the English Premier League. Just ask a player like Eddie Johnson, who scored a ton of goals in the MLS but failed to latch on at Fulham.