You're right, that's true.

It's not the ideal metric, but it's one that is realistic to compute with limited time and resources. To analyze that statistic using a growth metric like "largest 30 day average contributor gain" across such a gigantic dataset, consisting of hundreds of millions of rows and tens of millions of unique repositories, requires resources and engineer time which few people possess. We certainly don't want to divert too much of either of those things away from development of CodeCombat just for a fun data science experiment!