Ziggs has an extra nuke

I used ziggs ult right as I died and it went off did some damage. I respawn only to find the cooldown reset which was strange. I didn't use it and nor do I have footage

edit: sorry for bad explanation I was in a game, so heres a better more concise one

I got ganked in my lane and managed to escape with a sliver of my health, they dived me and so I ulted so they would take a lot of damage and heck maybe get a kill since it was early. I respawned to have the ultimate seemingly off cooldown, considering it was a useful ult especially against my match up I decided it would be best to keep it. I went awhile without using it so I'm not 100% sure if it DID reset the cooldown OR it's just a visual bug