It's not a scam; the number of backlinks doesn't equate to the authority of the link. A single link from CNN, for example, will increase a site's DR by a lot more than a link from some anonymous blog that has no links to it. The DR figures are supposed to replicate in a rough fashion Google's PageRank calculations, so reading about how PageRank works might be helpfu.
That being said, such third-party metrics aren't used by Google, and, in my experience, don't correspond that well with what's actually happening in the search engine results. I've never used any of these kinds of metrics to make any kinds of decision yet, and I don't recommend that you do, either.
AHREFS is mostly helpful in finding link prospects who might link to your site and for doing keyword research. People sure love to put a lot of stock in these third party metrics, but they vary from tool to tool, and none of them replicate the calculations that Google engages in.
Randy Ray
A good traveler has no fixed plans and is not intent upon arriving. -Lao Tzu