You should have been given an explanation, even if it was "for technical reasons", so that is not good. There are numerous reasons why they would have turned around but most likely they couldn't continue under ETOPs due to failure of something. If it is something non-critical, but would stop you going oceanic, then landing at the nearest airport (like Shannon) isn't the most useful option - better to go back to a base where you have engineering and company support coz they have engineers there and can have spares on the way as soon as the pilots call company to tell them of the problem.