Ok, so what did I misunderstand in OP sentence "no differences, we pronounce them all é and we don't care."? "them" is not referring at all possible accentuation of the letter e?

You did not misunderstand what they wrote, it’s just that what they wrote is wrong (and you are right).

Some accents use é when standard academic French would use something else. For example, in "j’ai été fêter ça", the 5 sounds "ai", "é", "é", "ê", and "er" could sound pretty much the same. But AFAICT there is no local accent in which both the "ê" in "fête" and "fenêtre" sound like "é". Certainly nothing mainstream.