Apparently they found recent grads with very large student debt load but commensurately high future earning potential had inaccurately low credit scores.
Credit scores measure the risk of future default based on past borrowing behavior. A borrower's credit score is not "inaccurately low" if there is little to no past borrowing behavior to apply the credit scoring model to.
Lenders can and frequently do take into account criteria other than credit score, such as income, when underwriting loans. In some lending markets (mostly commercial), individual consumer credit scores aren't even used.
That Earnest and other upstart lenders are choosing to more heavily weigh factors other than credit score is not particularly interesting. The true test of their underwriting criteria will come in the next down cycle. Having worked in this space, I should point out that there are many consumers with high incomes (or high earning potential) who are vulnerable. As such, I'd suggest that income and earning potential alone are of limited use in underwriting. It's not uncommon to see borrowers with high incomes who also have very low credit scores because they were over-leveraged and had serious negative credit events occur.