It’s often expressed that way, but a more accurate way to say this is that in legal proceedings an accused is entitled to a presumption of innocence, which means (among other things) that the burden of proof falls on the prosecution, and that failure to testify cannot be construed as evidence of guilt.
I think this is saying the same thing: not that the person is necessarily innocent, but rather that he is entitled to a presumption of innocence in legal proceedings.