I think it's hilarious that anybody would sell for 21.40
It means they think the price will drop below 20.45 ex dividend(you have to account for transaction costs too). That is risky seeing that this one is on the move increasing the regular. You can't give me cap gains argument either since it IPO'd this year.
Cys, which cut its div, went on the rise on exdiv day. I hope that is a harbinger for the restuvus on festivus.
I suspect you made a profit too, did I get some of those at 21.38 this afternoon? If this is as high as it will go pre-div, I think we can look for a quick price recovery after the dividend adjustment. At this low price it should be an easy hold for the div.