First off, congratulations on a very well handled EFATO.
Personally I think a slug of water in the fuel would explain what happened. The engine injested solid water which would have killed it instantaneously so when you thought it was at idle it had actually quit and was windmilling. As the prop windmilled the water got sucked through the engine and when it got gas again it started running at the commanded (idle) power setting by which time you were probably in the short strokes of the PFL