Considering the security forces had no idea whether he was working alone or what was happening, they obviously didn't think they could rely on the metal fence.
Look, I'm all for a free Palestine and I agree that what is happening in Gaza is a genocide. I also think that voluntary membership in any American or Israeli law enforcement makes them complicit in the heinous acts perpetrated by American cops and the IDF, respectively. I don't know you, but I'd guess that you and I agree a lot more than we disagree on these issues. I'm just saying, from the PoV of the security forces at the Israeli embassy, this was a potential threat to the embassy and their job is literally to prevent threats from harming the embassy. Without any further information to go on, their decision to draw guns first and get the extinguisher second is reasonable.