I work for a footwear company and I happen to know that some of the factories we use also make other brands. It does not mean the quality is the same.
The factory only constructs the shoes, it does NOT make the materials used (outsoles, leather, linings, hardware) nor does it come up with the design.
If the factory is capable it can make very similar looking shoes at both extremes (low and high end).
Still doesn't mean that Nike knock off is going to perform similarly to the real thing.
Of course some of the so called higher end brands also take short cuts and some of those shoes are made of the same exact crap as the stuff you see at Payless or Wal-Mart
I imagine it's the same with guitars.
Just because one factory makes different brands doesn't mean they will all perform the same. Different specs, designs, materials.