Help me understand how my family members paid so less.

I’m not an American, but I moved here a few years ago. My cousin and her husband had been in the US for approx 10 years when this happened. Their 2 year old daughter had leukemia. (Blood cancer)

She had a weeklong hospital stay, some surgery to inject chemo into her spinal fluid for which she was anesthetized, daily steroids, some IV chemo.

I just casually mentioned to them that it must’ve been expensive, their daughter’s hospital stay that week. They said it barely cost them $50-100 extra. They had company insurance. I think it was my cousin’s company covering for all 3 family members. Both work in California.

How was it so less?

ETA: They’re in the US on work visas. Not citizens/permanent residents.