They used telescopes to infer that this planet has a specific molecule on it that is known to be made by life on earth and not en masse by any other process.
IMO this is a stretch because life on another planet probably has somewhat different chemistry. There is a massive unfounded bias in all pop exobiology that finding other life means finding stuff just like life on earth.
Which is not to say it isn't neat but it is literally another planet light years away. We know almost nothing about it.
Except they are already vibes based so there is no reason to think the initial approximation is accurate. They could all be massive overestimates. There is no reason they need to regress to the mean.