That wasn't prompted by the Israeli airstrike, it was pre-planned and initiated by Hezbollah. You seemed to have missed Hezbollah's statement, so I'll repeat it for you:
Hezbollah has said it hit 11 Israeli military sites, fired more than 320 rockets and sent drones flying into northern Israel on Sunday as part of the “first phase” of its response to Israel’s killing of the movement’s top commander in a strike on Beirut last month.
Hezbollah said its attack involved more than 320 Katyusha rockets aimed at multiple sites in Israel and a “large number” of drones.
It later announced the military operation was “completed” for the day. The Lebanese group denied that Israel’s pre-emptive strikes, launched just before its own attack, affected its own operation. “The enemy’s claims about the pre-emptive action it carried out, the targets it struck and its disruption of the resistance’s [Hezbollah’s] attack, are empty,” Hezbollah’s statement read. It added that all drones were launched as scheduled “towards the desired targets”.'
You can read about it in the Guardian if you like.