All microfiche diagrams I've seen have the nut on the brake side.
I don't see how it could matter much as long as all associated parts are flipped as well.
I wouldn't lose sleep over it, but I do think I'd switch it around.
Now, having the nut of the sprocket side might make removal of nut a little easier for some. Since you're on the sidestand side of the bike.
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2008 WR250X
Gearing: 13t - 48t
Power Commander 5 / PC-V
Airbox Door Removed - Flapper glued - AIS removed
FmF Q4
Bridgestone Battlax BT-003rs