EOB shows "billed amount" vs "allowed amount" - why is there a $3,200 difference and who eats that cost?

I had a colonoscopy last month and my EOB just came in. The hospital billed $4,800. My insurance shows an "allowed amount" of $1,600. My EOB says I owe $480 (my 30% coinsurance after the deductible). But what happens to that $3,200 difference? Does the hospital just write it off? Does my insurance secretly pay it? I'm genuinely confused.

I called my insurance and the rep said it was "contractually adjusted" but wouldn't explain further. I called the hospital billing department and they said the same thing basically. Nobody will give me a straight answer.

I'm also nervous because the anesthesiologist billed separately and I don't know if they're in-network. The EOB for that hasn't arrived yet. Should I be worried about a surprise bill on that one?