Let ML be the difference between Mastodon and Linux, and Twitter and Windows differ by ML too. That reflects the original sentence.

Let's call MT the difference between Mastodon and Twitter.

From the first sentence, Linux is separated from Mastodon by ML, and from Twitter by both ML and MT, and from Windows by ML, and MT, and ML again. But because Twitter and Windows difference is analogous but opposite to Linux and Mastodon difference, we can ignore them, so Linux is separated from Windows by MT, the separation of Mastodon to Twitter.

Which is exactly what the reworded version says.