Looking at these bulletins, they appear to be quick summaries of pretty much any nuclear related incident that happens in the US, no matter how minor. I would assume that these are mostly intended for public transparency, and as for a quick reference point for regulatory action. Introductory slide on a PowerPoint sort of material.
In that context, I'd guess that the 300 CPM figure is just a signpost that says "we measured the worker to make sure that he was safe to release to a hospital."
In that context, I'd guess that the 300 CPM figure is just a signpost that says "we measured the worker to make sure that he was safe to release to a hospital."