There is a simple TestNG class with two methods so that 1st method has group "group" and 2nd has group "apigroup".
Run tests with command:
Both tests are run.
Only method with group "group" is run.
Demo project could be found here: https://github.com/khospodarysko/testng-groups.
Looks like the issue is in GroupMatcherMethodSelector as looking at includeMethod it is seen that is always returns true.