Yikes! While nobody should be riding with the quick release open, the non-brake side seems a better place for the QR lever on a disc brake bike, even if only to reduce the risk of burns from accidental contact with a hot rotor.
I found it interesting that Shimano's illustrations for their Alfine DH-S501 dynamo hub with center lock disk brake show the QR lever on the connector (non-brake) side, whereas it was shown on the brake side on their older DH-3D72 model. I'm not sure what their primary reason for the switch was.
There has been some discussion about QRs gradually coming unscrewed on disc brake equipped bikes, especially on mountain bikes (see this article by James Annan). So if the lever ended up loose, it wasn't necessarily someone forgetting to tighten it after reassembling the bike after transport or a tyre change.