On non-dwarven runecraft; the dwarves know they aren't a dwarven invention. They believe that Thungni discovered and copied pre-existing runes, he didn't create them. That means they pretty much know that someone else invented them and created them before the dwarves reproduced them. Any runesmith also knows that they don't understand how runes actually work, that they're black boxes that runemsiths duplicate without understanding them.
The old Albion book directly tells us that the Old Ones taught selected dwarves there how to make runes who then went back to their people to pass the knowledge on.
The later may or may not be the case here, but the former certainly is.
Now, the strictures of Thungni's Cuit several thousand years in the future make it very clear that sharing dwarven knowlege with non-dwarves, particularly with human rune masters, is forbidden, but in the present day that rule may not have become so ironclad. If, for example, a dragon flies over from Albion, asks where Grungni and Thungni are, and casually reveals that they were taught runecrafting alongside the pair of them by the same teachers, that may produce major theological problems in the Cult, but it won't necessarily result in a crusade to kill them.
There's gonna be many, many pointed questions about the parentage of a dragon who turns out to have the bloodline of Thungni running through the dragon's veins.
If dragons can shapeshift into forms that can interbreed with humans, they can presumably shift into forms that can interbreed with dwarves, and those in turn may be able to reproduce with other dragons to eventually produce dragons with a small amount of ancestry from Thungni.
Note how the foundling ruensmiths work. Potential runemsiths don't need to prove a heritage from Thungni to be taught, it's just assumed to be present in all those with the Gift.
Given that infidelity is presumably something that can happen with dwarves, and the general destruction of records during the Chaos incursion, there are probably many dwarves descended from foundlings who are potentially descendants of Thungni. As time passes, the proportion of dwarves this applies to will presumably increase.
Of course, taking that precedent and applying it to dragons is, let's say, a bit of a stretch, but if there ever are any dwarven equivalent of the Cathyan dragon-blooded it may one day become possible.
Rather unlikely though, even if the Northern dwarves extend the precedent of Snorri's shard dragons and the Eastern dragons develop a greater alliance with the magma dragons, neither of those are known to be able to assume humanoid form.
