This stunt by coca cola targeted their audience so well, it suprised me it hasnt been done more often.

The key points here are that they make the vending machine a more interesting object in the cantine. Usually the machine is something people pass by and only use if they are in need of it directly.

After one person getting a free drink, the machine offers more and more - spreading the 'love', to be cliche.

Obviously everybody who witnessed it was too excited to notice what was happening, but they were happy due to Coca Cola's doing. Subconsciously Coca Cola have made them see that they can get more than they need. Coca Cola have shown how they offer more than you need and will go further to make you happy, making them a desirable brand.