… then you look at the fine print: https://jetpack.com/support/jetpack-stats/free-or-paid/
«We define a commercial site as one that you aim to make money from. This could be through advertising or affiliate links, selling products or services, soliciting donations or sponsorships [...]»
So if you are a Free Software developer that is inviting donations or sponsorship for your work, you're also a commercial site according to them.