I answer my 'phone when cycling if I think it's safe. When it's my wife or a good friend I yell "I'm on the bike!" in a failed attempt at comedy.
I stop if it looks like it's going to be a long chat. Often people hear me puffing away and cut it short as they know where I am.
Sometimes I let it ring out - if I'm fixed-gear on Euston Road between a bus and a white van... never a good place for a private chat.
Once or twice I've made a call from a moving bicycle, but usually off-road or on an empty rural A-road.
Similarly, I get snacks out of my back pocket while moving, unwrap Mars Bars (surprisingly hazardous) and drink from my bottle.
When I was a motorcycle courier I answered my radio on the bike (shouting through a full-face, of course).
Sometimes people will overstep what many will see as the mark, but I'm not sure your Youtube transgressor was doing anything terribly naughty.
In truth I thought his restraint was quite admirable, coupled as it was with a slightly bemused look.
I'd be inclined to take that clip off Youtube.