Your shell will expand the wildcard to include 斑马家族2.jpg, and ack *always* searches regular files that are provided directly on the command line.
Rob's answer here is correct. I didn't notice the * at the end of the path. Files specified on the command line are always checked, and directories specified on the command line are never skipped, even if you have options telling ack to do so. The general rule is to let ack do as much on its own as it can.