This is insane, there are so mny zombies in the late game that it becomes insanely difficult to play

I guess it autoconfigured that since I have no memory of doing it myself

That is because it can be configured to be downloadable through Synergy instead of separate install.

I can go in custom maps and select a ravenholm map

In what way? What do you mean?

i haven't subscribed to this, yet i still can play it... Hmmm

In your Synergy custom folder, do you have the 692269416 folder? If not, you have to copy it from the workshop folder over to there. If you do have it, you could try maybe moving the ravenholm.dat from Synergy\synergy\custom\692269416\content to Synergy\synergy\content
Then check in your console when you start up Synergy, there should be a section when you scroll up that has a bunch of green and brownish text saying either:
"ContentLoader[CL]: Found SourceMod 'Ravenholm' in ..."
or "ContentLoader[CL]: Not loading content 'Ravenholm' ..."
There is also a section higher up that says the same thing but with SV instead of CL.
Using the info there, you should be able to tell if it is possibly loading the sourcemods folder from somewhere else that you may have to move or link Ravenholm to.

I can't see Ravenholm on my map list! Why?!

lol