Well maybe he realized how ignorant you are about who he is. Assuming that cutting off contact with someone is "cultural" Polish thing? this is simply ignorant statement. News flash! it happens everywhere!
I told him I might be busy and could call him the next day but he insisted I call him.
indicates that something happened that made him upset.
So if Polish person cuts off contact, first thing that comes to your mind is ooo it's because he's Polish.. this is so dumb of you.. not, maybe he found out something about you that made him resent you and simply doesn't want to have any contact with you, (he might be non confrontational type). Maybe he was secretly in love with you and you deliberately hurted his feelings somehow. Avoiding contact might be childish but calling it cultural?