Yeah, I had that same thought. A length of 4 or something seems unlikely to happen because a miner would almost have to be doing something nefarious to build o

Yeah, I had that same thought. A length of 4 or something seems unlikely to happen because a miner would almost have to be doing something nefarious to build on top of an already stale chain. A length of 2 could be some kind of concurrency/synchronization issue caused by one miner not having seen another miner's block in time to start mining on the "correct" chain.