This was a response for Israel bombing a place in Iran
Kinda worse, actually. Israel bombed an Iranian consulate in Syria. So they bombed Iranian diplomats (and consulates and embassies are, IIRC, legally part of the country that runs them) to kill someone that they said was part of the 7 Oct Hamas assault. That’s a really, really big provocation.
Keep in mind that, despite everything, the US still has an embassy running in Moscow. So, yeah, bombing a consulate/embassy is a Really Big Fucking Deal.