Captain Love: It's just one man.
Don Rafael Montero: It isn't just one man, dammit! It's Zorro!
Three Finger Jack: Hey, basura! Up here! Well ain't you a sight for sore eyes. Full grown vultures walking around like real folk. Welcome! Welcome to Hell's outhouse! Now they call us the disappeared once but as you can see we ain't exactly disappeared. We've just been a little hard to find.
Captain Love: You. I know you.
Three Finger Jack: You bet you do, peckerwood! I'm the legendary Three Finger Jack and you are a bunch of murdering trash dressed up in fancy sweet smelling doodads!
Captain Love: Ignore him gentlemen. He's a common thief.
Three Finger Jack: Hah! As common as they come, but I ain't nothing to you "gentlemen." I steal gold. I steal money, but you... You steal people's lives. So damn you, and damn the whores that brung you!
Diego: You're a thief, Alejandro. A pitiful clown. Zorro was a servant of the people, not a seeker of fame like you. Buffoon.
Diego: Is it finished?
Alejandro: Yes, Don Diego. It is finished.
Diego: Not for Zorro. There will be other days, other battles to fight. That is your curse and your destiny.
Diego: Your brother is dead! We lose the ones we love. We cannot change it. Put it aside.
Answer: He recognized that Bernardo was really Diego de la Vega and he realized that the young Zorro he had seen earlier could not have been Don Diego. He then deduced that the new Zorro looked similar to Don Alejandro (and was probably warned by Captain Love that Don Alejandro was hiding someting) and made the decision.