No - I'm sorry but there is absolutely nothing funny about it!
Putting pictures like that on the net and thus implying that it is a good idea funny and cool or entertaining or WHATEVER to keep a goldfish in a SINK is down right idiotic.
Would you think it humorous if they had a kitten stuck in a fishtank or something? Just cause it's 'temporry'? Now think of all the idiots who would visit the site, see that picture and decide to try it for themselves.
Would you put YOUR fish in the sink if you were realy a responsible fish keeper an take photos of it swimming around in circles because you want someone out there to consider it funny and try it out for themselves? The de-chlorinator and fish food indicates NOTHING about these peoples' resposibility - that photo does.
And about putting the two bettas together in the bathtub - there's a prime example of the sort of people who, having seen this, would buy a cheap little feeder goldfish and put it in a sink or flush it down the toilet for kicks. These aren't people with a sense of humour! These people are sick!