It’s because they tried to brute force it.
With incursion rats on grid who scram and Web and dish out a considerable amount of dps. All you need to do is pop one or two logi cruisers and it will cause a fail cascade in very short order.
Sure you might not get all of them. But you will get a good number.
Attacking an incursion fleet is not the same as ganking a freighter or a miner. It is a full fleet of very blinged out (and generally high sp) battleships with logi support and boosts.
Treat it like a fleet fight, only with Sansha being a 3rd party.