Some stands can be controlled in different ways. Devos pointed out that the type of Stand that Polnareff has he wouldn't be able to see. He has more of a raw close short ranged fighting stand with a lot of speed. Devos stand on the other hand may not be be that strong in a physical fight it is better with tricks like possession which he has full control over whether he is at a range or not.
In regards to Devos's whereabouts he managed to escape to a different bathroom. He never fell off the balcony because Polnareff stated that he didn't see his body (and we didn't see it on the ground). The officers were trying to link the murder of the Room Service guy who was killed and Devos which was in another nearby area in a bathroom. So it was easy for them to link it all back to Polnareff.