In states that have expanded medicaid, they have seen some low wage workers get shifted from private insurance to medicaid, which reduces the amount hospitals are paid. So if you consider the private insurance rate to be 100%, the medicare 70%, medicaid 30%, and uninsured the same as non-paying, for every patient that move from private health insurance to medicaid you have to have two move from non-paying to medicaid.
I would assume for most hospitals, you'd see more than 2 medicaid patients gained for every 1 private insured moved to medicaid (or whatever the actual ratio needs to be; in reality it would depend on what services are involved, but I would guess it would range from somewhere north of 1:1 with confidence, but no clue what the high end would be; I would guess less than 4:1 but not with a ton of confidence). I think if you pressed people making this claim they would say that expanding Medicaid makes it harder to politically get a fix that "works" rather than actually claiming that the net result is negative in the short term.