You guys clearly don't understand how internet advertising works.
The main player in the Internet advertising world is google. Google keeps tracks of all your searches and web browsing history, if you use gmail it also checks whats in your mail. Using this they then create a profile for you and target you with specific ads.
Websites sell space to google, and companies sell their ads to google and ask them to target certain demographics. As such Emirates has probably given their add to google and pprune has signed up for google advertising so anyone who meets the demographic criteria for an emirates ad see's it on the pprune website and on other related websites.
For example, my dad is a experienced pilot, when he logs onto Gmail he sees ads for airlines searching for captains, I on the other hand am a new graduate from flight school, as a result when I log onto Gmail and Pprune most of the ads I see are for flight schools and type rating courses.
Google is basically running the internet now and with the advent of skype it will be able to collect all the information it wants on you and target you with specific ads. Facebook does the same, hence all the ads you see on the fbook website are targeted at you as a result of all the information you give them, i.e. location, age, and all other info.
Hence Emirates might not specify PPrune for advertising, but has asked Google to put their ads in the right places, and PPrune has signed up for Google ads and hence the two, PPrune and Emirates, were paired up using Google logic.