The one where you yourself even say it's O(n)? Big-O is concerned with asymptotic complexity. It's O(n) until you show us it's not (e.g. implementation code, not musings.)
Here's my second reply to him, where I myself point out that idealized Von Neumann machines don't exist in real life, and certain idealized O(n) operations (such as memcpy) may in real life for any possible "n" be cheaper than some baseline constant C (such as the cost of a Ruby method call): https://news.ycombinator.com/item?id=18988075#19001585