https://stackoverflow.com/questions/7840087/what-does-callable-typehint-mean is a duplicate question of https://stackoverflow.com/questions/7839763/what-is-callable-typehint-in-php, which is closed as not-a-real-question. This is the first time I've encountered this on StackOverflow. Is that normal behavior? It seems very odd to me.
The question marked as "duplicate" could more precisely be called a "double-post". That is, the asker of the first question has simply reposted the earlier question. When that happens, comments and a close-as-dupe are usually used to draw attention and encourage/force the poster to follow preferred procedure and revise the earlier question. It's irrelevant to the duplicate closing that the original was also closed.