Did Juan nick the idea? And if yes, is that a problem?

In my opinion, he's probably never seen it, and it's definitely not a problem.

Why? Because an idea is not the same thing as a piece of film. An idea is the connection between the images and the product.

Example: take the footage for Guinness 'Surfer', and change the endframe to 'Visit Cornwall' (Note for non-Brits, Cornwall is a UK surfing destination). Now the ad is predictable and quite shit. Because what makes it great is (among other things) the unexpected connection between surfing and Guinness.

The connection between a drumming gorilla and a shop having a sale is quite unexpected, I grant you. Actually I quite like the ad, though the execution is v. shonky. But it's nowhere near as interesting - or dare I say it profound - as the link Juan creates between a drumming gorilla and a bar of chocolate.