Double-spending just means spending the same output in multiple transactions--there are many ways to perform a double-spend attack. Your interpretation of a 51%

Double-spending just means spending the same output in multiple transactions--there are many ways to perform a double-spend attack. Your interpretation of a 51% attack is correct. If it wasn't clear, my comment was referring to a double-spend that would result in an invalid block i.e. both transactions are on the same chain. I simply used an example to argue that it's always been the case that invalid chains are rejected by honest nodes.