Well, I looked it up again and found this:
Mark 6:30: And the apostles gathered themselves together unto Jesus, and told him all things, both what they had done, and what they had taught.
31And he said unto them, Come ye yourselves apart into a desert place, and rest a while: for there were many coming and going, and they had no leisure so much as to eat.
32And they departedinto a desert place by ship privately.
33And the people saw them departing, and many knew him, and ran afoot thither out of all cities, and outwent them, and came together unto him (KJV)
So the gathering WAS spontaneous, Jesus didn't even send the disciples out to attract them. The crowd gathered on it's own.