Granted both are done to create a misrepresentation of the level of buying and/or selling interest in a given stock.....but there is still a difference.

When there are bids being taken out by hitting them and taking them out with an aim to dropping the PPS using short selling.....that's one thing.  

Its something else when shares are swapped between the accounts of one market player as is the case with wash trading. 

My own view on wash trading is that it is a strategy (and an illegal one at that) used to boost volumes in an effort to draw interest into a stock....