  Black hole accretion discs can produce powerful outflowing plasma (disc
winds), seen as blue-shifted absorption lines in stellar and supermassive
systems. These winds in Quasars have an essential role in controlling galaxy
formation across cosmic time, but there is no consensus on how these are
physically launched. A single unique observation of a stellar-mass black hole
GRO J1655-40 was used to argue that magnetic driving was the only viable
mechanism and motivated unified models of magnetic winds in both binaries and
Quasars. The alternative, X-ray heating (thermal-radiative wind), was ruled out
for the low observed luminosity by the high wind density estimated from an
absorption line of a metastable level of Fe xxii. Here we reanalyse these data
using a photoionisation code that includes cascades from radiative excitation
as well as collisions in populating the metastable level. The cascade reduces
the inferred wind density by more than an order of magnitude. The derived
column is also optically thick, so the source is intrinsically more luminous
than observed. We show that a thermal-radiative wind model calculated from a
radiation hydrodynamic simulation matches well with the data. We revisit the
previous magnetic wind solution and show that this is also optically thick,
leading to a larger source luminosity. However, unlike the thermal-radiative
wind, it struggles to reproduce the overall ion population at the required
density. These results remove the requirement for a magnetic wind in these data
and remove the basis of the self-similar unified magnetic wind models
extrapolated to Quasar outflows
