Why does Hot water come from a cold water faucet?

Because someone switched the lines or labeling. <

1- Someone installed the piping not bothering to read modern codes requiring water hot and cold to be 6" apart

2- C/W supply to a tank or other heat source does not have the 27" heat trap (loop) to prevent stratification of hot water molecules entering the potable water supply

3- Failure on the part of an installer of appliances that use both hot and cold water supply to have an air gap or vacuum breaker or the very least a check valve

4- Cold water lines picking up ambient heat from the surrounding air or close contact to heating lines

5- Cross connections see #3