They 'checked' it meaning they looked to see if the PS fluid was topped off? Or that they actually did a flush?
Also, don't assume that the dealership did the flush, look on the service receipt or ask the SA. You really can't trust the dealership too much. Just because they're a dealership, doesn't mean they ALL know about the inner workings of BMWs. Heck, I'm willing to bet that some enthusiasts on the forums are more knowledgeable than some certified BMW techs, to be honest.
'08 AW E90 335i
PROcede V5 | BMS DCI | RR DPs | ETS FMIC | FORGE DVs | Stett CP | Vanguard | PSS10