I assume "Earth like" in this context means planets that resemble the only planet known to hold life at least enough to be capable of holding life themselves. The problem is we don't even know what that means exactly. It's also assuming that life can only exist in "Earth like" conditions.

Also, if Fraction of Earth‐like planets that develop life = 1 and Mars is an "Earth like" planet, are they assuming life evolved in Mars too or something?

in that case, value of 1 for "fraction of Earth‐like planets that develop life" is odd since we are far from confident that life ever developed on mars.

What we call atmosphere in Mars would pass for a very good vacuum in a classroom. Life could develop on a Mars sized body, but then the star would have to be far less active than our sun (so that the planet could retain a reasonable atmosphere)