Makes (a small amount of) sense -- the only high-quality tubes I've ever seen were either manufactured in the U.S., Europe, or in various parts of the former USSR; Chinese tubes have a very poor reputation at least in audio circles.

Perhaps this is because nobody ever bothered to put a serious effort into outsourcing vacuum-tube production, in the same way ICs and microprocessors have been outsourced, leaving the remaining production still domestic?

Or maybe it's just that there are huge stockpiles of the things sitting around in the U.S. and they're slowly being sold off, both for domestic consumption and export, but the net result is an export of tubes? That wouldn't be hard to believe either.