"This man" refers to Peter. The speaker probably did not know Peter's name.
## he is a Galilean ##
Matthew [Matthew 26:73](../../mat/26/73.md) says that the people could tell Peter was from Galilee from the way he talked.
## I do not know what you are saying ##
This idiom is used to say very strongly "What you said is not true at all" or "What you said is completely false." (See: [[rc://en/ta/man/translate/figs-idiom]])