What exactly does the LogisticRegression.predict_proba function return?

In my example I get a result like this:

[[ 4.65761066e-03 9.95342389e-01]

[ 9.75851270e-01 2.41487300e-02]

[ 9.99983374e-01 1.66258341e-05]]

From other calculations, using the sigmoid function, I know, that the second column are probabilities. The documentation says, that the first column are n_samples, but that can't be, because my samples are reviews, which are texts and not numbers. The documentation also says, that the second column are n_classes. That certainly can't be, since I only have two classes (namely +1 and -1) and the function is supposed to be about calculating probabilities of samples really being of a class, but not the classes themselves.

What is the first column really and why it is there?