I think there may be a probabilistic argument for some of these points. While a sample size of one is not much, it's more than none. We know we have life on ou

I think there may be a probabilistic argument for some of these points. While a sample size of one is not much, it's more than none. We know we have life on our planet, so we know it's possible in an earth like environment. So the only evidence we have points to earth like planets being more likely. The interstellar space craft is of course possible, but since we don't have any ourselves, but we have radio for a while now, it seems more likely that the signal originated from a planet, since the interstellar space craft is much more complex technology for which we don't have evidence yet.