It is possible that what you experienced was a result of an erroneous trigger of the autonomous emergency braking system. AEB systems have been known to be triggered in error and can be caused by debris in the road or a shadow, dirt blocking the operation of the sensors or a fault with the calibration of the system. While it can be irritating or even alarming, a system that is overly sensitive is more use than one which is not sensitive enough, as the latter could fail to operate in a genuine emergency situation. Keeping any bumper or windscreen-mounted sensors as clean as possible is one step you can take and you can enquire with your dealer about having the system recallibrated.