[defrost]

That'd be from your PoV.

It's been in low level general use on forums and IRC by non US english and ESL speakers since pre-WWW Usenet in my experience.

What has changed is I've recently seen it and close variations crop up here on HN, a primarily US forum, more and more in the past few months.

That'd dovetail in with your observation, but it's not a new coinage nor is it exclusive to disgruntled US residents by any means.