Even more live chickens are kept as egg layers, and as a breeding population. That's a lot of chickens.

Lab-grown meat is cultured from tissue samples taken from real animals. So, it is real animal meat. It's the larger-scale texture of specific cuts that they are trying to replicate. When successful, there will be no need to slaughter tens of billions of animals. But, I don't think production is anywhere near large enough to affect the market yet. Similarly for milk produced from genetically modified yeast in big vats.