Stonecunning: This ability grants a dwarf a +2 racial bonus on Search checks to notice unusual stonework, such as sliding walls, stonework traps, new construction (even when built to match the old), unsafe stone surfaces, shaky stone ceilings, and the like. Something that isn’t stone but that is disguised as stone also counts as unusual stonework. A dwarf who merely comes within 10 feet of unusual stonework can make a Search check as if he were actively searching, and a dwarf can use the Search skill to find stonework traps as a rogue can. A dwarf can also intuit depth, sensing his approximate depth underground as naturally as a human can sense which way is up. Dwarves have a sixth sense about stonework, an innate ability that they get plenty of opportunity to practice and hone in their underground homes.
It's a fairly small bonus. Passive search is nice, but a nat 20 on a skill check isn't an automatic success. Search is int based, and dwarves don't get a bonus to int, and their favored classes (cleric and fighter, apparently) aren't classes that are likely to dump a lot into int. We have seen very few int-class dwarves, if any.

A typical secret door has a DC of 20. I don't think this secret godly weapon has a mere " typical" secret door. If we look at the dungeon rules:

Secret Doors

Disguised as a bare patch of wall (or floor, or ceiling), a bookcase, a fireplace, or a fountain, a secret door leads to a secret passage or room. Someone examining the area finds a secret door, if one exists, on a successful Search check (DC 20 for a typical secret door to DC 30 for a well-hidden secret door). Elves have a chance to detect a secret door just by casually looking at an area.

Many secret doors require a special method of opening, such as a hidden button or pressure plate. Secret doors can open like normal doors, or they may pivot, slide, sink, rise, or even lower like a drawbridge to permit access. Builders might put a secret door down low near the floor or high up in a wall, making it difficult to find or reach. Wizards and sorcerers have a spell, phase door, that allows them to create a magic secret door that only they can use.
A well-hidden secret door has a DC of 30. Even with the dwarf bonus, 5 ranks in search, synergy bonus from knowledge, a 10 int dwarf would be unable to detect that.

And I mean, technically, the search DC is up to the crafter. A godly relic might demand even better than "well-hidden". The DC could be 40 or higher. Dwarfs do also get a +2 to craft with stone. And there's synergy bonus possible there. Maybe they set the DC all the way to 50+?