He means what if some of the other patrons had guns. The perp knew the police were armed and used the element of surprise to neutralize them before they could really retaliate. However, if one or more of the cafe's other patrons had been armed, they could have eliminated him then and there. Possibly saving the life of one or more of the officers.
I would love to be able to carry but getting your permit in California takes an act of God.