What key observation made by Antonio Paris's research strengthened the comet theory regarding the 6EQUJ5 signal?

The frequency drift observed during the 72-second burst matched the expected Doppler shift

The supporting evidence for the comet theory, as identified by Antonio Paris, was found in the analysis of the signal's movement over the 72-second recording period. A moving source, like a comet traveling across the sky relative to Earth, causes a Doppler shift—a measurable change in the signal's observed frequency due to relative velocity. Paris found that the frequency shift observed during the burst perfectly aligned with the calculated Doppler shift expected from an object moving at a rate consistent with a comet passing through the telescope's view. An artificial, stationary transmitter would not exhibit this specific type of frequency variation.