Was it an error? All depends on the pressure....and whether both 6000ft and FL60 existed. I've never been any good at these altimetry questions - I'm sure you know if it's high or low pressure that will give you the right conditions for both FL60 and 6A to exist.
There's a second issue that varies between States of whether the Transition Layer is a minimum of 1000ft 'thick'. Some States have procedures that ensure any altitude allocated below the Transition Level will be separated from any FL that is allocated above - others do not.
I think the 'must say altitude' thing, although good practise, is a bit of a UK thing.