By my read, this is the core of the articles argument:

But if these billionaires’ largesse was designed to retain the conservative judge on the country’s highest court, the donations might fall outside of the definition of tax-free gifts, which according to the Supreme Court must stem from “detached and disinterested generosity.” If the benefits showered on Thomas were designed to elicit court actions or job decisions, they could be considered taxable income, whether or not there is definitive proof of quid pro quo on Thomas’s part.