My guess is that while it may have measured in the official tests as not harmful, they must have had some indication that wasn't the case for the entirety of the shrimp or I don't believe they would have issued this recall.
They also wouldn't tell customers to just throw away the contaminated products if that were the case; radioactive materials do not belong in household trash. The fact that nobody is concerned about spreading contamination further through improper waste disposal suggests that this is nothing more than the usual unscientific fear-mongering.
Ya, I see tons of lightbulb manufacturers making sure people don’t toss their compact fluorescent light bulbs in the trash. Certainly companies don’t do things like dump harmful forever chemicals into rivers and oceans. They would never dream of understating a hazard and letting people throw away evidence of their mistake. Walmart was just being overly cautious because they error on the side of public health. Everybody knows that.