If he really has to go to jail and it's not some probation type of thing that does seem ridiculous.
To me it seems incredibly unlikely that a two month jail sentence will be carried out. Even if it's a real sentence, most European countries lack the resources to put such petty criminals behind bars. Worst case scenario in Belgium would be that you are given house arrest really. Perhaps France is more strict, but I doubt it.
Either way, he appealed and the prosecutor didn't even ask for jail time, but the judge thought it wise to go above and beyond the prosecutor's proposed sentence. This is obviously going to be overturned anyway.