My first thought was “WTF”, but then I considered the problem. You can grow beef cells, but only easily in a thin layer. So, get something porous but edible, and grow the cells all over it. Rice is just an obvious choice from a culinary perspective.
It’s weird, but I bet cooked up as a burrito or casserole this could actually be appealing, and it’ll be way easier to commercialise than more traditional meat shapes.
Edit: So, here’s Nature on the same. As usual, popsci left out the gotcha, and that’s that there’s not actually a significant amount of beef there. Rice is only slightly porous, just as it seems, I guess.