Cultural or psychological differences in interpreting facial expressions. It's clearly not despair to me. The mouth is upturned, which indicates smiling.
But to someone who can't easily differentiate upturned from downturned, it might be despair.
In blown-up version like this it's easier to see the upturn. In smaller renderings, like in Facebook & Google products on my desktop and on the phone (or pixelated copy-pastes of it on top of Facebook videos), the rendering sits squarely in the uncanny valley for me. It looks like smiling, but then it looks also like the face is in great pain, with all the muscles contracted, squeezing tears out of its tear ducts.
I suppose the guy who I'm responding to is expecting you to be familiar enough with the full selection of emoji to know that it's definitely the tears of joy emoji and that there isn't a nearly identical one for despair.
It'd be a poor design decision if there were. But it's also unreasonable to expect everyone to think like a good interaction designer.
