He said he was worried that your poorly written EULA might get HIM in legal trouble. And that’s why he wanted a refund as he’ll likely not use it either way due to this. I think you mis-read his plea in every way possible and took it as a threat and in return threaten him.
This is nothing but amateur customer support, probably the worst customer support scenario I’ve seen thus far. And this is why a lot of companies refund ‘those customers’ because backlashes like these can and will do more harm to your company than good.
It’s a shame because the software looks very professional. I sincerely recommend you look over how you handle these kind of issues in the future.