And he went out, and followed; and he knew not that it was true which was done by the angel, but thought he saw a vision.

So Peter followed him out, but he was unaware that what the angel was doing was real. He thought he was only seeing a vision.

and having gone forth, he was following him, and he knew not that it is true that which is done through the messenger, and was thinking he saw a vision,

And going forth he followed [him] and did not know that what was happening by means of the angel was real, but supposed he saw a vision.