The article leaves out details about how exactly “underpaid” and “market value” are defined for this purpose. Perhaps Paysa at https://www.paysa.com/ (from which the article gets its information) may have more detail.
But the list of companies may be of more interest. The list of companies in the most-likely-to-be-underpaid list does include a number of companies considered “desirable” in other ways by employees, who may be willing to take a lower pay level to work there (Glassdoor, Pinterest, Microsoft, Dropbox, Facebook, Airbnb, Uber), although it also includes a major outsourcing company that hires lots of H-1B visa holders (IBM). The least-likely-to-be-underpaid list includes companies that are seen as less “desirable” in other ways, so they may need to offer higher pay to attract employees (Netflix, Walmart, Yahoo).