Did this guy always have so much gold to barter with? He has over 20,000. The only other person to have even half that amount (riverwood trader + investment perk) might be a glitch, I'm not sure. This is awesome, I'm about to sell master neloth all sorts of stuff that will inevitably annoy him.
Is he supposed to have that much gold?
If you're seeing it with the Riverwood guy, yes it is a beneficial investment perk glitch for you. Apparently it's random. (For instance, in a game where I had Invest, Riverwood didn't have 20K but a couple of others did.)