Just as it says: He healed them all.
All is the people who followed Jesus as he went back to Galilee and went up to the top of a hill. Australians would probably call it a mountain, because a hill doesn’t have to be very big here to be a mountain.
How long was the walk and the hill climb that followed? How committed to finding healing from Jesus were the people in this crowd for them to have followed Him that distance? Perhaps they were all healed because it was the seriously committed who made it to Him.
Matthew 15:29-30 Jesus returned to the Sea of Galilee and climbed a hill and sat down. A vast crowd brought to him people who were lame, blind, crippled, those who couldn’t speak, and many others. They laid them before Jesus, and he healed them all.
Even with the faith to follow Jesus and ask for healing, seeing the results was still amazing:
Matthew 15:29-31 The crowd was amazed! Those who hadn’t been able to speak were talking, the crippled were made well, the lame were walking, and the blind could see again! And they praised the God of Israel.