My take: 'Technical' derives from the word 'technique'.
Technical drummer: Usually used to describe someone who has extremely masterful grasp of various techniques (odd time sigs, crazy speed, dexterity, rudiments, limb independence, etc) and is usually involved in playing music that showcases/embraces technicality.
Head to youtube, search and watch videos of the following: Virgil Donati, George Kollias, Thomas Lang, Mike Mangini, Marco Minnemann, Vinnie Colaiuta. You might have a better idea after that.
That said, it's just another way for people to describe drummers.
Sometimes 'too technical' is used in a negative sense by people who prefer 'groove-oriented' drummers.