What does callable typehint mean? is a duplicate question of 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.