Mostly it seems to be because they're making a federal civil rights complaint. Gross negligence and civil rights complaints tend to defeat immunity, though I don't know if that'll be successful against the city itself.
If they can prove malice on the city's part, immunity goes out the window. And they may be able to do that.
If the case gets that far they lose. It's always about proximate cause and I promise you, a jury will decide that the raid was proximate cause. Surviving motions to dismiss based on immunity or venue and other stuff is where this case really will be decided. And where the appeals will be directed.