I don't either. Perhaps it is colloquial for 'they are flesh and blood', as in all men are mortal. Or are we talking about Big Macs? Do you have any context?
It's title of a story. This is an example in the story.
"They're made out of meat."
"Meat?"
"Meat. They're made out of meat."
"Meat?"
"There's no doubt about it. We picked up several from different parts of the planet, took them aboard our recon vessels, and probed them all the way through. They're completely meat."
I seem to have seen this story elsewhere. Are the speakers machines? I believe they come across humans ('carbon units'?) and can't believe that such sophisticated beings can consist of 'meat', i.e. as MrM says, 'flesh and blood'. Machines naturally despise flesh and blood.
Things are 'made out of meat' when the meat is fashioned into a shape.