Why George John Brown Used an Alias Golding

Was told by a Sharon, who was doing the family tree but she is tracing a daughter of George's - Catherine GOLDING
She found a "permission to marry" entry in the Tas.pioneer archives for a George BROWN and Bridget O'BRIEN.
Did he choose BROWN because it was common,or was it a family name?
Now Sharon has got me thinking lol...so any information on this mystery would be wonderful.