There will be more than 2. They are commutation events caused by the brushes connecting to the new segments on the commutator. It depends somewhat on the number of segments on the commutator, tiny DC (toy) motors generally have 2 brushes and 3 commutator segments (to 3 coils), so you get 6 pulses per rev.
6! That makes no sense to me. Can you explain please? Thanks for the link, but all it says on actual RPM measurement is: Speed measurement is best performed by measuring the number of pulses over a timed period and not by measuing the time between 2 pulses!