Point 1. Enriched Uranium wouldn't make much of a dirty bomb. It's simply not that dirty. A real dirty bomb would be made with fission by-products like colbolt 60 etc. That stuff is hot, hot, hot, while you could take a nap in enriched uranium and not be harmed.
Point 2. Where in the hell would the Congo get the ability to enrich uranium? Maybe the author is confusing enrichment with refining (i.e. yellow cake) but actual enrichment is way way beyond the capability of the Congo.
Bottom line. This story is bunk.
Exactly. Both isotopes have low specific activity. Plenty of people worked at the Hanford Reservation, etc. and are just fine.