My medicare summary for appendectomy is quite weird.

This summary, from Medicare.gov, is for everything, including surgery, surgeon, anesthesia, and pathology. Seems there's $18,000 missing…between the approved amount vs what they paid provider, and my estimated obligation. I'm 99% sure they mistakenly have the same amount for billed and approved, since approved should be much less, but even so their computer should show me owing 18,000 more since it doesn't add up?

FYI was outpatient so Part B covers, and I have high deductible supplement, and supplement site shows like $100 as my obligation, so not sure who bills me that the $986 "you may be billed" amount shown in link? Do I pay that to medicare, ie expecting a bill from them, since doesnt seem like the Supplement paid that? New to medicare…so is this common, that there's a mistake like this? Or am I the one making some big mistake?