Saleh is a Youtuber. Apparently he has a significant following. Regardless, exploiting a subject that the main stream media is sensitive to is an excellent way to get more attention. Right now the mainstream media is on the lookout for hate crimes. Mr. Saleh is on the search for more subscribers. Manufacturing and/or embellishing this event was a perfect way to get more subscribers and reach a wider audience.
Those who have capitalized on the current trend of being famous by being famous will do anything to get into a news cycle. Right or wrong, this guy wins because his name, face and youtube channel are all over the news now. He would say or do anything to keep getting clicks.
Yes, Saleh was exaggerating his claims regarding Delta, because the other passengers on the flight say that Saleh's story is not the way it happened. The other passengers report that Saleh and another man were shouting things in Arabic. So it's not because they were speaking Arabic, but rather that they were loud and disruptive that were kicked off the flight.
Given previous incidents involving Delta Airlines and Muslim passengers which are not entirely dissimilar to the incident described by Adam Saleh then it seems totally possible that he was telling the truth. It appears that Delta Airlines stiffly penalise their Muslim customers for even the most trivial act and tend to support white passengers even when they are being unreasonable.