I thought the same thing. A quick google search shows a pretty large variation in reported statistics depending on what's being sampled.
W3Techs checks the top 10 million sites on the internet and they report something close to 1/3 Windows, 1/3 Linux, and 1/3 unknown Unix. My guess is that a fairly large chunk of unknown Unix is Linux.
W3Cook checks the top 1 million sites, and they report 2% Windows and 98% Unix.
Basically every brick-and-mortar business with more than a couple of computers has a Windows Sever domain controller and Exchange server in a closet somewhere. It does not generally host the website.
And some of those servers on the public internet are only nominally public. Their names might be in the DNS database, but they're really an "extranet," that can only be used by authenticated users.
These numbers will become even harder to pin down as Microsoft converts the Windows Server business to the Azure cloud.
W3Techs checks the top 10 million sites on the internet and they report something close to 1/3 Windows, 1/3 Linux, and 1/3 unknown Unix. My guess is that a fairly large chunk of unknown Unix is Linux.
W3Cook checks the top 1 million sites, and they report 2% Windows and 98% Unix.