The term "reverse" is not the right word to use. What is meant is that you can generate another input for which the SHA1 output matches your other SHA1 output. This is because SHA1 has collisions.

So "foo" could hash to 1 and "bar" could hash to 1 also. It doesn't mean 1 means foo, but it means if your password is foo, bar works too when hashed and compared against a stored hash.