Okay, so both bikes are welded steel. But so is the Soma Smoothie, made of Reynolds 853 air-hardening steel and very lightweight. So the category "welded steel" has a lot of variety within it. But in this case, they're pretty similar. 830 is cheap, 520 is overbuilt for touring so it may have similar gauge steel.

They both use cantilever brakes.

The geometry will be slightly different. Mountain bikes usually have slacker head angles, and a larger amount of trail. But the 520, being designed for touring, will have slacker geometry than your typical road bike, so closer to mountain-bike geometry at least.

And of course, wheel size.

But on the whole, not huge differences. I expect the 520 frame to be better-built, somehow, just based on the pricepoint, but I don't know what the actual differences are.