If you assume for the moment that the suspect fire bottle is indeed from MH370, is there a possible scenario wherein the fire bottle was ejected by some some sort of explosion/fire on board yet the aircraft continued to fly on for some distance?
Given the current hypothetical flight path for MH370 it appears to have turned south almost due east from the point where the bottle was found. Perhaps such an "event" (if such an event is possible) caused M370 to unexpectedly alter course and turn south. Prior to the tun south, MH370 appeared to be following known way points, yet it suddenly turned south and flew in a straight line along no established route. This might explain both the presence of the bottle (again, only if it is from MH370) and account for the satellite pings. Just a thought . . .