What are negative and positive after potentials?
Yes, you are correct. The negative current is hyperpolarising the axon and the positive current is returning it to baseline from a hyperpolarised state.

They are often referred to as inward/outward (negative/positive respectively) currents as well, due to the direction of the flow of ions. Which is further compounded when you start looking positive/negative ions.

Inward currents are inflow of +ve charge, or outflow of -ve charge.
Outward currents are vice-versa.