So we know exactly what happened with that bitcoin double spend transaction. It was a weird situation where an attempt was made to raise the fee on a transaction but the original transaction succeeded instead. 1/5

I do consider it a double spend. A valid transaction that someone could have seen as being confirmed was later orphaned by a conflicting transaction. But it's reasonable to not agree that's a double spend. 2/5

It's arguable whether it's an RBF instance or not. Someone could have relied on the first transaction, even if they were aware of RBF. But it was the low fee of the first transaction that allowed the second transaction to be relayed. 3/5

Most importantly, there is nothing fundamentally new or surprising about this. Everyone was aware this could happen and nobody would advise relying on a low-fee transaction with only one confirmation. The only use cases this would affect are impractical and inadvisable ones. 4/5

So, technically interesting but no big deal. It does underscore the bitcoin blockchain's uselessness for low-value, high-speed transfers. But the transaction fee levels probably did that already anyway. 5/5