French prosecution over insecure WiFi?

I have been following the conviction of a Frenchman over downloading two Rihanna music tracks http://www.bbc.co.uk/news/technology-19597429, and I came across this article from PC World http://www.pcworld.com/article/262313/french_piracy_law_claims_first_innocent_victim.html that in the article claimed he was convicted for an insecure WiFi network.

In the article it states "Though his wife admitted, in court, to illegally downloading two Rihanna songs, Alain Prevost was still fined for failing to secure his Wi-Fi network." however it does not follow up on what this meant.

The article goes on to say he was convicted under a French anti-piracy law known as HADOPI (Haute Autorité pour la diffusion des œuvres et la protection des droits sur internet), not a law dealing with WiFi networks.

It would of been interesting to know whether the WiFi was insecure?, did his wife/ex-wifi illegal connect to his wifi? Did he not change the encryption key after separating?  

Does lead to the through what happens when partners seperate and they have been using WiFi, the encryption key should be changed to prevent the ex-partner from reconnecting and downloading illegal material as revenge.