You're right about the first two papers (which used the same approach). Ruling out a FP result would be difficult, which is why it wasn't fully embraced by the scientific community.
The third team took a different approach [1], with results that are both more accurate, less prone to FP, and generally agree with the other findings.
> Here we report observations of two absorbers of highly ionized oxygen (O VII) in the high-signal-to-noise-ratio X-ray spectrum of a quasar at a redshift higher than 0.4. These absorbers show no variability over a two-year timescale and have no associated cold absorption, making the assumption that they originate from the quasar’s intrinsic outflow or the host galaxy’s interstellar medium implausible.