In order for the ruby to drop in the first place atleast one person in the party has to be lvl 30. So people who farm/mine in here as a lower lvl job would obviously never see one drop. This is why the ruby COULD drop off these leeches and not too many people would find it here. Also only three leeches spawn at a time and with almost a 7-10 min respawn there are much more effiecent areas to try for this drop.
From the many forums that I read through when SMN came out with Zilrat everything said it drops off Leech family. And this still holds true with all the forums today. There has never been an offical update from SE (atleast to my knowledge) to change where you can obtain the ruby.
But like I said before there are many other areas like Dunes, Qufim, etc where the leeches are still relativly lower lvls and much more abbundent.