Seems kind of unlikely. Britain was able to produce pots before the Romans and I'd bet a lot of the pot-makers when the Romans were here were indigenous. Yes, there may well have been a loss of technology (don't see many hypocausts or viaducts dating from the post-Roman period) but to the point of not being able to make a pot?

More likely graves were dug to look for loot than cooking pots, I'd have thought.