I, too, am completely skeptical of these stories. Here in Oklahoma, we have the locally famous “Heavener Rune Stone” situated on a similarly remote outcrop. Probably an 1800’s hoax.
Nonetheless, there are indeed Europeans making their way into China as early as the Bronze Age. Anthropologists were taken aback with the red-headed mummies in China’s Tarim Basin who fit the description of the tall blue-eyed giants of Chinese lore.
There was a theory that the Mandan Indians were Welsh and came over with Madoc, but few scholars believe that now.