From the BBC link you posted the only claim that I can find is that, and I quote:
Israel claimed a number of Hamas and Islamic Jihad militants had been killed in the incident, but it has not provided any evidence or further explained the threat to its troops.
Israel's Foreign Minister Gideon Saar earlier this week echoed the army account, saying "the IDF did not randomly attack an ambulance".
The IDF promised to investigate the circumstances after a surviving paramedic questioned its account.