In my opinion ... Horsey is a ludicrous chess figure, a jester for lichess.
www.merriam-webster.com/dictionary/jesterSynonym from Horseplay
www.merriam-webster.com/dictionary/horsing%20aroundHorsey is like Monkey.
www.merriam-webster.com/dictionary/monkeyHorsey on one's back.
Synonym from dupe ...
www.merriam-webster.com/dictionary/foolSome like to horsey around with posts to joke about the subject.
Only a horsey would say something like that.
It a response to stuff a post with glee, when the other icons don't fit.
A he, ha, he, ha response, which is the sound of a donkey or horsey.
Is it a mascot?