X265 theoretically does better compression. But that depends on how much we're compressing.
It looks like the x265 copy is just that much higher quality, which is perfectly indistinguishable on any mobile device.
I wouldnt be surprised if some of the difference in filesize is audio quality.
Seems they're walking it back?
https://abc7news.com/post/anthropic-cannot-good-conscience-accede-military-use-ai-ceo-dario-amodei-says/18651096/