Hello there !

Although this is not at all my area of expertise, I'll try to help a bit. Since I can easily access French documentation, I may be of assistance.

First thing to consider is that even though there does not seem to have been a big all out assault on this precise day, combats were still happening in northern France at the time and in neighbouring regions of Belgium too (see 2nd Battle of Ypres/Ieper and Battle of Hill 60). Obviously, people die in sporadic or lower intensity combat too, not only in big all out assaults. The fact is big troops concentrations have to have been around since the Battle of Artois started 2 days later, which means a great concentration of troops on both sides (and potentially some early fighting/skirmishing).

Second thing is that people tend to take some time to die. And they can be moved from one hospital to another too. Maybe he was wounded earlier and "merely" expired in an hospital in Northern France.

I hope that may have helped and that, even though the answer was not quite in-depth, it may have been of some use !