This seems like a particular definition of "flesh" that's not particularly germane to meatness. Lab meat is made of the exact same animal cells that regular meat is, the tissue just happens to never have inhabited an animal. When we eat meat, we don't value the fact that the cells we're eating were once part of an animal, we mostly value the taste.
It seems to me that this isn't a necessarily property of meat but a contingent one caused by the fact that meat used to only be possible to produce from animal flesh.
>When we eat meat, we don't value the fact that the cells we're eating were once part of an animal, we mostly value the taste
You'd be surprised. We even have different names and preferences for different age stages of the animal, different varieties of the animal (regional etc), etc.
Those distinctions exist because of the perceived impact on the tastes and textures of meat. Not because of anything such as ethical preferences to old/young animals.
It seems to me that this isn't a necessarily property of meat but a contingent one caused by the fact that meat used to only be possible to produce from animal flesh.