The plugin guy can afford to be reasonable-ish. It reduces the likelihood of the scam being publicly disclosed, and I'd wager that 99% of people never notice the plugin is doing this.
Oh come on, it's not a scam and he's not stealing anything. It's clearly mentioned on the license and it's up to the users to go through it (like any other open-source plugin or software they use). At the end of the day the plugin creator was polite, understanding and returned money back even though he was not obliged to do so. It's a win-win situation as they clearly describe it, but the OP wasn't satisfied with the high (30%) percentage.
How is hiding 2% in your wiki (instead of in LICENSE where it belongs), and then taking 30% instead of 2%, not a scam? If someone listed a price of $2 for a burrito and then charged you $30 at the register, you would not consider that OK.
It looks to me that the plugin author isn't only trying to get the money he's owed from people who are trying to scam him. Which still isn't a great thing, especially since it can happen mistakenly, but it's at least a little more understandable.
Is it though? A settlement in a civil case is money in exchange for not pursuing further civil legal action.
A situation of "we're giving you money so that you don't report a crime" (which is implied by "turning in to the authorities") is more like extortion/bribery than it is a settlement.