"Police quoted witnesses who saw a man walking into the clinic with a paper bag, which he put on the floor, right next to a heater by the reception desk, and kicked it. Liquid poured out, caught fire and the whole floor was in flames and smoke."
Don't really need to be an expert in starting fires.
Let's say a lot of them are garbage and you only hear about the rare occasions it works. Let's say 10% of the time the fire is good enough to kill.
Two stair wells means only 1% of the time you get a kill.
Lighting two fires is also harder, you need more planning and stuff. So that probably equals out a bit for the better fire lighters.
If it's Mossad doing it then sure it's possibly similar.