Being from a Muslim family strict about eating only Halal meat, and only ingredients derived from Halal-slaughtered animals, I have a split opinion on this issue. (Essentially, I am “non-alcoholic” pescatarian when eating out or at the grocery store.)
First, as a person who was raised to read ingredients labels, I understand someone who wasn’t conditioned in that way can never be as diligent in this matter, no matter how much that person loves food. Knowing this, there’s always a probabilistic guilt assigned to situations.
If a person was like me – fairly strict, very specific and attentive – I would tell that person my mistake. The person might think that food product is okay for them, and might continue to eat it. As an example, my cheesemonger told me a certain cheese didn’t contain animal rennet when it did. (Should’ve known cause it tasted too good.) We kept purchasing more and sharing it with people. Eventually saw that same cheese at Whole Foods labeled as having animal rennet. Checked with the manufacturer to confirm. First time in 3 years our cheesemonger was wrong (we keep a list of all our cheeses and checked all of them again.) It was an honest mistake, but now we felt guilty cause we had fed the cheese to so many people who also avoid animal rennet. Say the cheesemonger had realized his mistake soon afterward, I would really have appreciated it if he told us immediately. Replace “cheesemonger” with “good friend” to make it a non-professional situation, I don’t feel it changes anything.
On the other side, you have so much randomness of things various Muslims are strict about: strict about Halal meat but not alcohol, strict about Halal meat proper but not animal-derived ingredients, considering Kosher to be Halal, considering any non-pork to be Halal, etc. It’s a mess trying to figure out what matters to someone. I have family members who don’t trust Halal meat stores, so they go and slaughter chicken and lamb themselves. Yet, these same folks will knowingly eat food with, say, Vanilla Extract (alcohol). I know strict Hindus who eat Parmigiano Reggiano (animal rennet), but they avoid gelatin. Then there’s folks with different rules for when at home and when going out. If you can think of a combination, it probably exists.
So for me, if I had to even ask myself once what to do, I would just leave it alone.
