Can’t speak for this specific kit but in general: A big problem with lab grown meat and cell tissue culture is that to grow cells in vitro you usually need fetal calf serum. That’s a liquid from, well, cow abortions basically, that contains a plethora of different molecules like growth factors and mediators. As far as I know, there is no vegan alternative to this yet. We are talking about a liquid here whose composition is really complex, so it’s a really big task to create a plant based FCS alternative that performs just as well.

Tldr: probably the set contains a liquid made from cows.