As we explicitly mention in the "Before you begin" section, example test cases are not part of the actual assessment. Example test cases are given for a better understanding of the points that will be taken into consideration during the assessment. You need to consider all the possible edge cases when submitting a solution. Therefore, it is possible to pass just example test cases without passing test cases that are taken into account while assessing your solution.
Please note that this doesn't apply to our real-life tasks that have all the requirements listed in the task description and your code is tested against them all - in this case you will always know how many test cases have passed.