DR is a number a tool vendor made up. That isn't a criticism of the tool, it's just what it is — a log-scaled estimate of how many links point at the domain, produced by a company whose crawler is not the one that decides your rankings.
Which means it is buildable. And once something is buildable and people will pay for the number, someone builds it. That's what a DR52 with 30 visitors is: it has been fed. Usually a couple of hundred links off other sites in the same seller's inventory, plus whatever's cheap that month, and the whole cluster props each other up. In 2013 the same guy was selling PageRank 4 blogroll links and it was the same conversation, right down to "traffic doesn't matter for link juice".
The catch you can't quite see is this: the only thing DR measures is the property the seller is manufacturing. It's a price tag, not a valuation.
Ask him for search traffic instead and watch what happens to the conversation.