It's part of a new swedish documentary about WWRY. Is this never-seen footage? For me, at least, it is. The clip above is all they show of the recording. If anyone is interested, it can be seen here, with the plus side of english spoken language NOT being overdubed, a rarity in most european countries, but still has swedish narration. link
Considering the multi-tracks only feature Frederick singing that particular bit (Maylor sing other bits, but not that one), I strongly suspect it's a staged video. Still nice to see, of course, but I remain sceptical.