Is meat still good when the package has expanded?

Probably not. If you've taken refrigerated meat out of the refrigerator and let it warm up some, the warming air inside the package could expand it, and your meat is probably okay. But if it's still refrigerated, the package expansion is probably caused by gases produced by the action of bacteria.

Almost always an expanded package is due to bacteria growth, the expansion due to warming the air inside the package will not be very discernible to the naked eye. Rule of thumb in the food industry is: "When in doubt, throw it out"