In external circuit it is observed that the flow of electrons takes place from Zn to H. Thus it concludes that the electrons must have originated from Zn i.e. it is oxidized and it is anode and it is negative with respect to hydrogen electrode. The standard oxidation potential of zinc is therefore + 0.76V.
What is the meaning of negative potential?
So, a positive electrostatic potential at some point means that a positive (negative) charge at that point will have a higher (lower) potential energy compared to the reference point. A negative potential means that a positive (negative) charge at that point will have a relatively lower (higher) potential energy.