@PlanDeRaccordement
No, don’t say anything. I’m sure he knows it’s not vegan or vegetarian and is eating it anyway. You don’t have to be 100% vegan in all things to identify as vegan. And some vegans do occasionally eat nonvegan for health reasons.
Urgh. No, actually you cannot “identify” as vegan if you’re not. It’s extremely offensive to vegans to do so, and a constant source of confusion, boundary pushing and and people disrespecting and misunderstanding our beliefs.
To be clear, vegan is the belief that animals are not here for human use. It is not a diet and it is not an “identity”. We avoid animal use as far as possible, accepting that we live in a non vegan world (for example many vegans make exceptions for medication, or for sitting in other peoples cars with leather seats etc). There is no inbetween in whether you believe that animals are for human use, or not. One is vegan and one is not.
There are no health reasons for eating meat. Health may be their justification, which is fine, but it is simply not a vegan choice. There are vegan ways of achieving the same thing.
In answer to OP, yes tell him. Just, “did you know that has milk in it?” is fine.
I’ve been vegan 15 years and still make mistakes, for example sometimes the same brand will switch packaging or change ingredients, so that things you’ve bought for years, or which look like the things you’ve bought for years, are not vegan. If it’s a mistake he will definitely want to know.
Alternatively, he may have bought this since before he was vegan and would rather use it up to not waste it, as this (in his mind) would be more disrespectful to the animals lives. Not vegan, and I personally would donate it on Olio, but I understand where that comes from especially if he’s not aware of how to donate.