This could just mean that all PII is handed off to another agency before it is stored. The NSA pulled similar shenanigans with public statements about their bulk data collection.

This isn't as strong a statement as it seems. It doesn't say that the machines themselves don't store PII, or that "AIT screening does not result in any permanent record of PII". There have been cases of body scans leaking (if I recall, the vendor was recording the scans within machines used by the US Marshals).

How have they defined "personally identifiable information?"