I would assume that the perception is there erroneously,.. and that any difference is on a micro level,. likely barely measurable.
The error in the assumption would be understandable. Because most electric motors can benefit from the higher voltage of 240, it is often assumed that motors wired 240 are more efficient. Again, this is not really true from an electrical consumption stand point, or power generated, but for a motor that can be wired either way, wiring it 240 will mean the additional voltage will help get the motor started faster. (start up demand is much higher than continuous running)
Therefore a motor wired 240 is "better" than wired 120. This idea has been assumed to mean that better equals more efficient.
None of that would apply to the power running to you car's charger.
Where 240 is ALWAYS "more efficient" is in power loss due to length of run/wire gauge. By doubling the hot leads, you can move twice as much amperage through a specific gauge cable because you have doubled the number of conductors.