Being warm enough is no evidence of life. Venus and Mars are both in our sun’s “Goldilocks zone” At the edges yes but still within the zone current theory expects life to exist.
There are lots of other questions that would need to be asked before asserting that life is likely there.
Does the planet have a magnetic field or is it blasted with radiation from its own sun and space?
Has the planet existed long enough for life to evolve?
Is the planet being bombarded with asteroids?
Another factor is that Gliese 581 is a red dwarf star with an estimated mass a third of that of the Sun. It’s light is weak and it’s heat output weak compared to the sun.