On their leaderboard there was an NT4.0 machine with several years of uptime. People accused the owner of having manipulated the reporting tool, but the owner said it was just being used as a secondary DNS server internally at a company, and scheduled to be replaced as soon as the hardware fails. I don't know whether that happened before the site shut down unfortunately.
But, it turned out there was a bug in our earlier agent version that wrapped the uptime at 365 days and all their servers were well over that. They'd had warnings set at a year and critical at 18 months/2 years, some high value.
I asked if they were worried, and apologized for the bug. They said it wasn't a problem and just increase the thresholds so it was all green again and they'd get around to rebooting at some point.
I tried powering it back online afterwards. It did not power back on.
The uptimed package they told you to install also exists on for example FreeBSD. And from the table it looks to be available on platforms like aarch64 (64-bit ARM), and powerpc too. (Unsurprisingly, given the very straightforward-to-implement thing it does.)
So to answer your statement: No, and no.
And all the program does is keep track of the highest uptime your system has ever had. And the website takes these records from users, and presents the submitted data online.
I dont think the website is even made by the same people, probably.
https://github.com/rpodgorny/uptimed for the uptime max stuff that runs on your machine, and all this website asks you to do is to submit your high scores from that other tool.
Whoever made that page should've had some better information.
Are you asking the owner of this website that takes data submitted by users to open source the website? Or are you talking about the above-mentioned program you have to run, which is already open source?