Both are shown as coming from Methyr Tydfil, Wales - although the address for Alfred's wife is shown as Troedrhiw

There is no conflict in the statement :-

Troedyrhiw or Troed-y-Rhiw, in the parish of Merthyr Tydfil

Its a mining area so a flow of people to and from Cinderford / FoD was happening.

Troed-y-rhiw (The Foot of the Hill) is a small town just 3 miles from Merthyr Tydfil in south Wales.
http://www.genuki.org.uk/big/wal/GLA/MerthyrTydfil/Troedyrhiw/
http://www.geograph.org.uk/search.php?i=3479982
http://www.alangeorge.co.uk/troedyrhiw.htm

just as a note :-
Cambria is the classical name for Wales, being the Latinised form of the Welsh name Cymru (Wales). So I guess the early settlers brought the name to Pennsylvania.

your family in 1911
1911
WILLIAMS MATILDA F 1878 33 Westbury on Severn Gloucestershire
WILLIAMS MAY F 1906 5 Westbury on Severn Gloucestershire
WILLIAMS WILLIE M 1904 7 Westbury on Severn Gloucestershire