It’s certainly possible the police are lying. It’s possible any report that says only a “knife” was found is incorrect too.
There are plenty of reasons to criticize their behavior in this case. I don’t see a reason to latch on to insisting it was only a regular pocket knife found.
It’s irrelevant, in other words, whether he was carrying a switchblade, a regular knife, or a bazooka for that matter. Once apprehended he had a reasonable expectation of safety. Obviously he was alive when apprehended with no injuries. Obviously he suffered some kind of traumatic injury after apprehension. There is no excuse for that. That is what should be the focus here.
We don’t know what kind of knife it was, and he shouldn’t have died as you said, no matter what type it was.
My only point is that this is a classic case about how false memes can be inserted into a conversation, if it turns out that “the switchblade” was an invention.