Albert Barnes Commentary Matthew 27:47

"And some of them stood there, when they heard it, said, This man calleth Elijah." — Matthew 27:47 (ASV)

This man calleth for Elias. This was done purposely to deride him and his pretensions to be the Messiah. The words Eli, Eli, they might easily pretend that they understood to mean Elias, or thus pervert them. The taunt would be more cutting because it was the universal belief of the Jews, as well as the doctrine of Christ, that Elias would come before the Messiah. They derided him now, as calling upon Elias when God would not help him; still keeping up the pretensions to being the Messiah, and invoking Elijah to come from the dead to aid him.

Or, it is possible that this might have been said by some bystanders who did not understand the language in which he spoke, or who might not have been near enough to hear him distinctly.