The short answer is Quill18, the long answer is WoW videos way back when. At the time I didn't really watch any youtube because its 99% garbage and was hard to find good content, but watching TB and Yogscast WoW videos back when I still played got me interested in their channels when they switched directions, since then have started watching JesseCox, Nerdcubed, Emmablackberry, JimSterling, GMM, Lindsey Stirling, Stuart Ashen, Northernlion, and just recently Quil18. So while learning of Quill18 was from watching NLs Cities Skyline video and then searching for more skilled game play to see if it was a game that I wanted, the reason I started watching NL was from TBs Charity water Stream where he covered many games including The Binding of Isaac.
So long answer summarized I found this game from watching Quil18 due to my interest in Cities Skylines which I found due to my interest in The Binding of Isaac which I found through my interest in Indie PC gaming which I found watching TBs WTF is series which I found from my interest in WoW which I started playing when a roommate was playing it in college. In fact most everything I find for entertainment now a days including TV shows like Doctor Who and movies like The Lego Movie (both because of Nerdcubed) all come back through TB.