The workhouse master probably had an arrangement to bury inmates in a cemetery in the locality of the workhouse in what was known as a pauper's grave. Such graves were not allowed to show the names of the deceased on a marker.
from the death certificate it states that the address is "12 waen terrace, Conwy, Caernarvonshire, Wales" and it sounds/looks like just a house? i can't believe there could be a possibility that he could have been buried with no mark or name
What was know as a pauper grave was simply a common grave, that is a grave not purchased as a private grave in which unrelated people may be buried.
Most cemetery regulations forbid the use of headstones on these common graves as only a few of the people buried in such graves had relatives who could pay for an inscription on the headstone.
The cemeteries also used these common graves to advantage by locating them between purchased plots, this gave the appearance that the cemetery was more spacious (or less packed) than was really the case.
You need to look in the plot register to see who was buried where.
I would also suggest looking in Bangor; many workhouses in a Union still used the policy of returning the body of the deceased to their parish of origin even though the Union was by this time considered to be “one parish”
Cheers
Guy