They will follow - but not identify - all bluetooth enabled smartphone and other digital niceties to have to have a clearer idea of how many people are in line or arriving to depart.
First there is no clear idea that they won't register anything somewhere.
Secondly it is just a stupid idea because it won't tell them anything. How many people have enabled their bluetooth ? Especially in an airport where social engineering and other attackers are - according to the hacker manuals - going around to find the CEO with much confidential data on the digital smartphone without any protection.
Another reason to cut it out.