What does it mean that in a point Α of an electrical field the voltage is -7?
There no capacitance added to the question nor distance As E fields are in [V/m] just a value with some equipotential plate or probe with very high impedance that gave you a voltage relative to 0V. Nothing else is implied, except assumed in some medium like  air or any electrolyte or dielectric or insulator. (All equivalent except dielectric constant which does not matter here)