It seems to me that people always miss the factor that ultimately determines the differences between self interest and altruism, which is intent. If an action is performed without thought for oneself, yet there is some result that aligns with self interest, that does not somehow nullify any aspect of altruism. Why? For one, people cannot predict the future. What may be perceived as good in one instant can quickly become horrible in another. Similarly, what is in one’s best interest is also subject to perception and changes over time. And finally, one is not always in control of the outcome. I would agree with you that for an act to be viewed as self interest vs altruism is a matter of opinion, when intent is unknown. However, whether or not altruism exists at all (because "it’s not altruism if they somehow benefit") is not - which I am not accusing you of making that argument, though it may be interpreted that way by some.