hmmmmm interesting... it's a page... so you should be able to tag them... even if you haven't liked the page ?!?!
I'll look into it and get back to you.
P.S. Are you using the website or mobile app? I know that sometimes I can't tag humans and other times I can't tag pages, depending on which one I'm using.
Re the video: Onto my 3rd try again today... 3rd time lucky I hope :-)