Habitable in astronomy just means it could have liquid water on its surface. Nothing wrong with calling it habitable.
Being tidally locked around a temperamental red dwarf used to be thought to be a deal breaker for life, but lately there is more debate about that. A thick atmosphere might spread heat around, for instance.
What’s interesting to me isn’t so much whether or not it has life, but how common earth-like planets in habitable zones are. We found one around the nearest star. What are the odds of that? Perhaps earth-like planets in habitable zones are much more common than we supposed.
I think the public gets caught out with the “only 20 years away!” part, not realizing that .2C is a LOT faster than anything we currently have. I think it would take a craft the speed of New Horizons (fastest thing ever launched from Earth, but maybe a Voyager is faster after some gravity assist moves) about 50,000 years to make the trip - for a flyby. Stopping once there is another kettle of fish. I’ve read about the laser powered nano-bot craft, that’s where the .2C comes from I think. Keeping a laser trained on something that small for long enough to get to .2C seems like a challenge in itself, but I absolutely support them having a go at it. If they launched today, I wouldn’t live to see the return signal, so that’s a bummer.
Well, we haven’t found planets everywhere. In fact, most stars, even a restricted subset of them such as very nearby stars, have not had planets detected near them. But that’s a function of our detection modes, which preferentially detect large planets near the stars. So yes, we may have to update that equation, but we need more data first.
As far as inhabitability, the formula doesn’t have much in it about the physical details of the planets. That’s probably intentional, but as we get more data, we may want to incorporate them. Everyone looks at the size of the planets, but how about the density of the atmospheres? I expect that few planets will actually have near-Earth atmospheric density. More likely they’ll have little or none (Mercury and Mars) or very high density (Venus).
So you’re wondering if alien astronomers have looked at our system and wondered? We’ve had chlorophyll pumping out way more O2 than we should have for like 3 billion years or more, so I hope they realize something weird is going on here.
Why their probes aren’t dropping out of the sky is another question.