Sure, the +0800 timestamps are definitely fake. A handful of timestamps that were later scrubbed show +0200 and +0300, though. And all the commits match 9am to 6pm working hours if you interpret them as +0200/+0300. The working hours even shift around correctly with the DST change.
The issue is that russia doesn't observe DST anymore. That leaves Bulgaria, Cyprus, Estonia, Finland, Greece, Israel, Latvia, Lebanon, Lithuania, Moldova, Romania and Ukraine. Very few of those have the infosec capabilities needed for something like this.
Jia Tan was registered in 2021, but first sprung into action during the buildup to the russian invasion of Ukraine 2022.
Jia Tan also used a VPN provider that's headquartered in the US. That only makes sense if they're in a US-aligned country, as using a US VPN would give the US more insight into what you're doing, and only protect you from other countries.
Personally, I'd guess that it was Israeli intelligence. But Finland, where the original XZ author lives, is another interesting possibility.