Congrats on asking the $64,000 question: the answer to which demonstrates that the numbers are almost certainly made up. The answer is 20, if you account for the alternative scores of 65% and 75% at post 21.
11/20=55%
13/20=65%
15/20=75%
BUT according to the linked article, Peterson, who got a 55% score, "moved to Iowa in 2009." How likely is it that 20 elections have occurred in Peterson's precinct since 2009? I suppose it is possible with school levies, etc., but I deem the likelihood very small. This assessment is reinforced by another poster on this thread, who says that caucus attendance is not recorded by the state. If correct, caucuses presumably would not be counted.
You’re right. I stand corrected. Must pay closer attention here.