"Zoi Da" originates from Zooey from Granblue Fantasy (ゾーイ, the community also will occasionally stylize her name as Zoi - completely coincidental).

She has many lines where she just says "Zooey Da!" (In her Japanese Voice Over). Really all it means is "This is Zooey, I am Zooey, It's Zooey" etc.

She says it a lot, so it's kinda just a phrase for her.

Around the time I was playing Granblue Versus (and I picked Zooey), I implemented some sound redeems, one of which was just a couple of clips of Zooey saying that. I kinda didnt expect people to be attached to it. But, well, a few years later and here I am still saying "Zoi-da"