Thanks a ton for your generosity, Austrobogulator, as well as for making things exciting!
I think, given that my pick 13 was not random, I owe it to people to comment briefly on my reasoning for it.
Firstly, it never really occurred to me that superstition might drive people away from it, something that in hindsight was probably a mistake. I reasoned from the bottom up, figuring that 2 and 3 were likely to be picked, possibly heavily, given lugum won the last such contest with 2 (which was second lowest then). Some people would reason similarly and then probably pick 5.
Now, the pick of 7 was actually revealed, which served as an important stimulus. Some, feeling the necessity to beat it, would have gone lower, to 5. Others would have opted for the next lowest prime, 11. The revealed 7 was likely (hopefully) already just one of several picks, thus negating the choice. This all leaves 13 as the first prime outside this convoluted chain of reasoning. Indeed, I was initially pondering the choice of 11, but the revealed 7 bumped it up a notch.
Finally, this was all speculative reasoning and, without knowing even the number of entries, could have been entirely off. I was banking on the two hour period yielding a fairly large number of entries, thus increasing the weight of the described patterns. If less than ten or so people had entered, my pick would almost certainly have been a dud.