I think it's clear the plugin author was/is happy to let the 2-30% stipulation fly under the radar and sit back and collect which doesn't sit great with me but also I kind of get it. I mean if you are going to take OS work and use it for your own gain (something I'm plenty guilty of myself I'll admit) then don't be surprised if not reading the license bites you in the butt.
In a perfect world OS devs wouldn't need to these methods to make it worth their time but we don't live in a such a world, people rarely donate to OS projects and expect issues/features to be added quickly and for free. People need money to exist and they don't owe you anything. Honestly if this plugin author had called out the 30% in their license I would say this blog author has no leg to stand on. As-is I'm glad the app developer got their money back and the plugin author should either stop charging more than 2% or update their license accordingly. But "stealing"? Too harsh, especially since you got your money back.