In this particular case, somone who did not know the situation taking the initiative to trigger the fire alarm would probably have caused EMS to be dispatched to the building where they were not needed at all.

If the building manager can trigger the internal fire alarm without causing EMS to be automatically notified, that would certainly help communicate that the building should be evacuated. I know that where I work, they use the actual alarm to conduct fire drills, but the FD isn't called, or course.

I'm wondering why they decided to evac the building - no matter what the cause of the explosion, it would probably have been better to shelter in place at least until more info was available.