Wow that's pretty bad. I could see that easily happen accidentally and lot of people getting screwed over by that once they are "caught".
As mentioned above, intent is everything. If it's caused by a fault in the meter and a load, which just happens to emit the right kind of noise for it to roll backwards, then you'll probably get away with it. On the other hand, if it can be proven you designed a device, specifically to emit noise, with the intention of causing the meter to roll backwards, then you can be done for fraud.
I also wouldn't be surprised if the power company could theoretically, get you to pay them, for any electricty they gave you for free, even if it was their error, but they would have a hard time proving it and it would have to be split up into reasonable, instalments, over a fair time period.