I am in Wales and have no access to Australian records, but I'm not surprised there were several William Thomases getting married there in 1930 - our forefathers were a bit unimaginative in their choice of names, unfortunately!
Billy left London on Dec 8, 1928, arriving in Sydney in February 1929. His parents may have been James Thomas and wife Mabel (nee Davies), though that is not certain. He returned to Britain in the last quarter of 1931. Hope this helps.
Regards,
Gareth