[anonym29]

That description is more about the power dynamics at play. H1b workers are often expected to work longer hours, and to do so with lower pay than American citizens, and not even think of complaining about it. In the US visa system, if an H1b worker loses their job, they have 90 days to get a new job (next to impossible when visa sponsorship is required) or else they lose legal residency rights and must either self-deport or be in violation of immigration law (which is a great way to screw yourself over on future opportunities). The resulting dynamic is one where both the h1b employer and the h1b employee know that the employer can basically ruin the employee's life whenever they want, for any cause (including no cause), at the drop of a hat. This shapes the working relationship in negative, coercive ways. That coercive aspect is the basis for describing it as "modern indentured servitude".