If you look at the documentation , it states:
Any Alarm
(Appears only when more than one Test column is shown.) The number of subgroups that trigger alarms for any of the tests selected under the Choose Test option. These are the eight Nelson tests and the test for Range Limit Exceeded.
So if a subgroup triggers at least one alarm, it is added to the total. However, a subgroup may trigger multiple alarms at once, and would contribute the same towards the total. The tests are not mutually exclusive.