I think it really was just a sincere question.
They do now, but in '98 when the iMac was released you were running Windows in an emulator with a big perf. penalty. You could run Linux with a bit of a struggle, though.
Once OS X was released they opened up Darwin in late 2000, but the iMac had been around for a few years then.
In '98 the first iMac shipped with MacOS 8.1, which was not open at all, though, and it took time for Apple to get on board with their Open Source strategy (though thankfully they did).
