I imagine that Premium Aquatics stores it in a system with natural live rock in the line ending up with "contamination" in the Real Reef Rock. I think the only way to be 100% hitchhiker free is to start from dry rock. Even then, the first piece of coral you add could have hitchhikers.
Nonetheless, I'd move any unidentified crabs to the sump or feed them to a mantis shrimp or puffer to be safe.
It is a violation of federal law to use this product in a manner inconsistent with its labelling.