I have a tire track eel that is about 22 inches long now, it was only a couple inches long when I bought it about a year ago, so they do grow fast
He loves big night crawler worms as well as raw pieces of shrimp and also sometimes eats raw chicken and fish when I have some to toss in. I've also seen him eat shrimp pellets but I think he loves the worms and shrimp the best. He lives in a 135 gal tank and rarely comes all the way out from under the big slate rock he calls home. He's never seemed agressive to any of my other fish in the tank and I have cory cats in there with him as well as other fish. He even shares his rock with 3 clown loaches and sometimes my golden algee eater lol
Tire track eels are great fish and fun to watch when they are out and about. Your friend should enjoy his, but he needs to remember they do get big so hopefully his tank isn't too small for a 20 or so inch fish.