I would say that it's Quora's problem. I thought they had some really good security but I guess not. But this time of year? Nothing really surprises me. I'm sure they'll get it cleaned up as most hackers always leave behind a "footprint" just to let them know they've been hacked.
Really, was it a fault from Quora side (or) from your side?
Quora is fault.
Nope, sorry that you had to deal with that.