Brain signals seem random

I have mentioned the Libet experiments, and the dubious argument against free will. Supposedly a brain signal shows that a decision can be unconsciously made.

Now new research claims to refute the experiment:

Jo et al say that these shifts are more or less random, spontaneous background changes in the brain – nothing to do with ‘readiness’ or decisions.

I am surprised that such a famous experiment could be so wrong. This is the main experiment cited by those who say that free will has been disproved.