Has that been done for a new release or something? I know they've done similar with other BBC shows over the last few years (Doctor Who being the prime example- even just with the SD releases in the 00s as there's still a massive improvement with modern transfers of the film even there, and the remastered Fawlty Towers is only SD too, even on the blu-ray release. Some or the more recent Doctor Who releases, Hitchikers Guide and Monty Python do have the newly scanned film material in HD though), doing new transfers of surviving film material (though in Bottom I think that only extends to the opening titles anyway, I think Bottom was entirely studio based, I can't recall any location work and if there was any it probably would have been on video by 1991).
Besides the opening titles, AFAIK every second of Bottom was shot on tape in a studio. There's one episode in the first series that's believed to be the pilot and the video quality is noticeably worse than the others. By the second series everything looks as good as a 90s BBC studio sitcom can look.
I'm a huge Bottom fan and it always makes me giddy when I find a few seconds of footage that's not been seen before, or is relatively rare. There's a short snippet of Bottom Fluff somewhere on YouTube that's been uploaded from the VHS release that isn't present on the DVD. I think the BBC logo on that tape has an extra bit of closing credit footage underneath it too, which isn't present on the final sequence.
There is, of course, a similar thing going on with The Young Ones. There's a noticeable drought of any bloopers or behind the scenes footage besides the odd very rare appearance on Auntie's Bloomers, and a smattering of YouTube videos that come from multi-generation VHS transfers that include some rushes from the more complex sequences in the show, like when Rik has a saw come through his bed.