Just to answer my own question, I learned later that the parameter into ActivateTriggerIn() function specifies the trigger bit as a value. Whereas when triggers are coming out, such as in isTriggered(), the mask parameter specifies each trigger bitwise.
So if I want to send trigger bit 4 in, I would indeed call:
And to monitor whether bit 4 has been triggered out, I would call:
which is the 4th bit has been set high. I suppose the rational is we only ever want to send one trigger in, but we may want to monitor multiple potential triggers out.