Time in grade is only a minimum requirement. There’s more.
Then how did he get promoted if he was a PFC when he took off? There's that other case of the guy in Iraq, Matt Maupin. He was a PFC when he was captured, was later killed by his captors, and a couple of years later when his remains were recovered the media was saying he was a Staff Sergeant. Does the Army just bump them up in grade on a regular basis on the assumption they'd have made that rank if they had served the whole period?