That's what it says today. Had Wikipedia been around in the 1800s it would have said that canals on Mars indicated an agricultural civilization. The point is that society has already processed the concept of alien life. We know how people will react because we can look to how they reacted in the past when scientists told them about alien life.

https://en.wikipedia.org/wiki/Martian_canals

Yes I remember children’s books I had as a child saying exactly this.

Finding something that "indicated" something is very different than "We went digging in Europa and found these alive creatures that look like Dolphins under the surface that live on Ammonia"

Society hasn't processed something we have no evidence of (yet), that doesn't make much sense. Ask "society" at large if they believe there are other species out there and most of them will say "I don't know" or "Probably not". In many places, religion is likely to be more believable to people than multi-cell life somewhere else than Earth.

That's an interesting take, but I'm not sold. It sounds a bit like claiming to be a family of firefighters because your grandpa participated in a drill once, passing along empty buckets.

My impression was that it seemed like a big intriguing maybe, not something like a verified fact.

A healthy chunk of the population believed, enough to impact national policies. Some of the first efforts at what we now call radio astronomy were attempts to listen for Mars signals. Just over a century ago "the big listen" saw large parts of the planet, including the military, turn off their transmitters in order to listen for Martians.