My ds definitely would have done the same thing on the math problem at that age. He loved, loved, loved algorithms and was less interested (at that age) in "number sense" or eyeballing the numbers to see if there was a shortcut. I don't know whether it's a gifted thing, but it might be -- if they can use the algorithm really quickly, they may not care for the common-sense, number-sense shortcuts that would save a less-proficient child the work? Just a theory…
By age 9 or so, though, ds had lots of number sense, so it may also be developmental -- what they notice at different stages.