Two ways this could be wildly wrong, both could apply:
1. The distance is much less than they calculate, meaning the radiated power is also much less than they calculate.
2. The object is not isotropic (radiating equally in all directions), but is instead creating a narrow beam aimed in our direction. Aka the flashlight effect. The initial miscalculation many years ago about AGN (Active Galactic Nuclei) was that they were isotropic, which would have meant the radiated power was ludicrous. Later they discovered black holes were driving the AGN we observed and the high power measured was because we were looking down the throat of the black hole jets.
You are probably more likely to be correct than wrong.
Based on using physics during my career as a mechanical engineer, I am well aware of measurement errors.