Obviously, if you compare the leading numbers of the versions 0.17.19 and 9.1.2, then you'll get 9>0, so the older version really does have the higher version number. The in-game downloader applies some more magic and only tries to download versions that are compatible with the Factorio version you're playing with, so if you are on Factorio 0.17, the game will ignore all versions for earlier and later Factorio versions. The key to this is the value of "factorio_version" in info.json. Perhaps you could suggest to the MMF author to take this into account before suggesting an "update" to an older version?
It is rather unfortunate that the versioning scheme has changed since this mod was first released. Then again, I believe it is good that TheSAguy switched to the current versioning scheme where the mod version number reflects the Factorio version the mod can be used with: It allows to keep more than one version alive in a clean way (see, for example "Bio Industries", where I've released updates for both Factorio 0.17 and 0.18).
Also, I just looked for MMF. I can't install it, however, because I'm on Linux and MMF is for Windows only. So there's really nothing I could do to help you: Removing the old versions would be the only way, but that's something I don't want to do (it's not my mod, I'm only helping out; also, it's nice to have something like an archive of old mod versions).