OK, I didn't notice that, that it did so well, in just 9 hours. And I don't have the answer.
But, since people on imgflip seem to have some kind of Pavlov's dog reaction to anything that has to do with upvotes, the way I envision it happening is maybe something like the following scenario:
The spamming got it enough upvotes (say 6-10) to be visible in the top 10 pages of Hot. From there, as people were scrolling, they reflexively upvoted it, because everyone loves things to do with upvotes, apparently. And that got it the 72.
That could be one way it happened, but I could be wrong.
Modda is asking the same question under the link on WiteRabid's Pie Chart, and supersaiynblueyasir has commented, if you want to check out what he's saying. I don't really understand his answers though.