Well, after 20 years of "OS 10"(branded originally as OS X, roman numeral 10, and all versions carrying the designation 10.something), Apple has just moved to OS 11, so it's not totally abnormal.
Of course, a few years back Apple dropped OS X and went to macOS, but kept the 10.x version numbering.
At least in the early betas too, there's some weird reporting with regard to version numbers. Apple's own software update/download utility calls it 10.16, although once booted it reports as 11.0. When I signed into my Firefox Sync Account, I had an email reporting a new sign in from "Mac OS X 10.0", which of course is an ancient(and terrible) OS.
At the same time, I too had understood that Win10 with recurring updates was supposed to be the "last" version of Windows.