Nasus can E twice in a row in Custom games

Hi, I'm a player on EUW level 30 and I was testing out the new caitlyn after the 5.22 update. I was in a custom game on my own with a handfull of bots and one so happened to be enemy team Nasus. I was in mid fighting the enemy team when I saw the Bot Nasus lay down his E, what then happened is that about 2 seconds after that he layed down another E right infront of the old E (you could see the old E dissapear it was still there when he casted the new E). Is this how it is supposed to be? He had 0 cooldown, is this a bug?

Regards,

Xanwing