If hit points are purely physical, yes. Because they are skill, luck, divine intervention, etc., they would not be able to pin down why it is that they are lasting a bit longer. There's nothing they can pin down as hit points. One fight they might last 5 rounds due to skill. Another fight they last 5 rounds not so much due to skill, but some luck and a cleric's god causing the enemy to stumble and strike a glancing blow instead of a killing one. There's no way that they can pin it down to purely them, assign any kind of number to it, and identify that as hit points.
That's actually not true. Variable damage means that 45 and 57 can go down at the same time, the 45 hit point guy first, or the 57 hit point guy first.