What floor were you on? I wonder if the security screening is for everyone all the time or only some people and/or only during peak times. I've stayed at the Hilton Doha a number of times, and usually am able to just walk past the screening to get inside without having to go through it.
Can't remember, maybe the 10th? Not sure how that is relevant though.
I went out in the morning and had to be screened on the way back. But (like the screening in DOH) the guy wasn't paying attention to the x-ray video anyway. Don't know about the Hilton, maybe they are allowed to let you through without bothering if they assess you as low-risk.