Yesterday's cactus was indeed Coryphantha vivipera. As to the confusion over the name of its genus, a respected botany journal has this to say:
The coryphanthas with pitted seeds often are segregated as Escobaria. That segregate, recognized by the International Cactaceae Systematics Group but not here, lacks the glands found in areoles of typical Coryphantha. Such glands are ephemeral.
Bring that up for argument over your morning coffee.