Possibly.I agree, he meant to leave it. Possibly the knife used wasn't a k bar..
But.... Ka bars are very large knives. Sheathed knives of any size ( I carry much smaller sheath knives for hiking) can be uncomfortable to painful while driving because they can dig into your side from the sitting position.
As a result, I am thinking that BK did not wear the sheathed knife in his car (I usually don't).
Rather, BK approached the home carrying the sheathed knife in his hand. In the heat of the moment, he un-sheaths the knife while dropping the sheath itself. The rest is too awful to think about.