Worried : ( Why is my 4 week old orphaned kitten bloated?

My daughter brought home a malnourished 4 week old orphaned kitten. I had him vet checked and dewormed and booked him for his vaccinations when he reaches 8 weeks. He is currently on kitten formula and recovery food. He has perked up and is now has the strength to horseplay around. He is voiding (peeing) and having soft bowel movements. According to the assessment the veternarian did on him, he is healthy. Is it the deworming medication giving him the bloating? Is he just bloated from gas? Is it something more serious or is this normal? Thanks for any information you can provide : ) Our resident house cat plays with him, we referee their playfights since we don't want the little one injured. The kitten was rescued on the brink of dehydration/starvation, a sibling of his succumbed to it's condition : (