Learn Spanish (Latin America): Volvió a pisar el casino.

In Spanish, a very common way to say you do something "again" is to use the verb volver (to return) followed by the preposition a and an infinitive verb. So, volvió a pisar literally means "he returned to step," but it is understood as "he stepped [somewhere] again."

Doesn't pisar usually mean "to step on"? Why does the translation say "stepped into"?

You are right that pisar literally means "to step on" or "to tread." However, in Spanish, pisar a place is a common expression meaning "to set foot in" or "to step into" that location. So, pisar el casino means "to set foot in the casino."

Is it also correct to say Pisó el casino otra vez?

Yes, absolutely! Pisó el casino otra vez or Pisó el casino de nuevo are both perfectly natural and mean the exact same thing. Using volver a + infinitive is just another very common, native-sounding way to express a repeated action.

Since volvió is the third-person singular form, how do we know it means "he" rather than "she" or "you (formal)"?

Without additional context, we do not know for sure! The verb form volvió could just as easily mean "she stepped into" (ella volvió) or "you stepped into" (usted volvió). The English translation says "he" because it relies on the surrounding context of the story from which this sentence was taken.