Because its very easy to edit it to make it look like the audience didn't laugh. All you have to do is turn down the audience reaction and add in some general white noise/background noise and you turn a clip of a joke that worked into one that bombs.

I'm not saying that actually happened but an interesting thing to point out here is that RT in its description has not pointed out what event this is from meaning we can't track down the source of the clip with ease (and most people wont).

As to the question of how is this Russian propaganda? Russia has been actively trying to make everyone in the West mistrust each other so that we focus on internal issues rather than geopolitics (what the Russians are doing).

Russia was a significant factor in fanning the flames of the antivax movement and as a direct result we have had measles outbreaks, and locations being shut down.

Calling it propaganda doesn't really work as terminology because it isn't really about making Russia look good, its about making us look bad and cause in fighting.

When they talk about digital warfare this is one of the aspects of it.

Does facebook and Zuckerberg deserve criticism/scrutinity? Of course they do, did this joke fall flat, probably given his past interactions but we don't know for certain it did and even if it did I don't want that information from a mouth piece from the Russian Government.