Since Queen was touring the UK at the moment, they could not appear on Top of the Pops.
So that's why they decided to shoot a video to accompany the song.
It was shot in one afternoon, using their rehearsal stage, and a broadcast-mobile from BBC-sports wich normally covered footballmatches.
Bo Rhap is considered the first music video ever, because it was the first video being shot with the purpose of promotion for the song. There are also some video tricks in it, wich were very simple, even for that time, and that also helped the video for Bo Rhap to be considered the first music video ever.
Thats the answer to your question dear. And no - I don't know either why certain Beatle-vids were not called the first clip ever. If you take a look at the video of " I am The Walrus " for example, it was really filmed and produced.
And if I had to be *really* honest : I would say The Beatles invented the music video. Not Queen.
But hey...you won't hear me complaining :-)
I can make a bigger bang than that dear <-)