Not totally correct
The fixed ELT is activated that way, but airlines may have also portable ELTs, some are activated with fluids (even urine) like water, seawater and they float, also have a self erecting antenna, others are handheld with push to talk feature! These portable ones are stored in the cabin for the flight attendants, or directly with the liferafts. Only a lurker here, but more than twenty years of breathing cabin air for a living!
I just hope that this freak story gets a proper explanation soon. My thoughts are with our colleagues, the passengers and all their families!!!