I don't think he's skinny but I am curious as to what the mark/lump is over his eye in the picture? Is this something on his body or is it a blemish on the glass/camera?
In addition to a good quality pellet and some occasional worms as treats, severums also enjoy picking at veggies. I put whole Romaine lettuce leaves in my severum tanks and they strip it all the way down until just the white stalk is left. They will also eat/destroy aquarium plants and eat the roots off of Pothos vines, so keep that in mind if you have any of those in your tank.