"electricity" and "free" are ambiguous terms. Overall, electricity has positive cost. Due to accounting practices and the cost of waste diposal, some electronics are negative priced for the user.

A better way to phrase it is that during short time periods "the cost of disposing electrons is greater than the cost of creating electrons" (and for technical reasons it's impossible to stop creating electrons in the short term) , so consumers can make money by offering electron disposal services to cover their electron consumption expenses.