Not necessarily. While they could just be "not opposed to it", and just don't practice altruism themselves, there is space in the OP's definition of what Good and Evil are for Neutral actors to actively oppose altruism, as long as they don't resort to murder, harming and oppressing altruistic people. They can morally oppose them and denounce altruism, they can deride them and make fun of them, they can banish them from their Neutral land (depending on whether one count that as harming) or just refuse to have anything to do with them, for example. There were real life philosophers who condemned altruism, yet never acted out on their conclusion violently, so they'd both oppose good and yet not be evil under the thread's definition.