I dunno how you use “Sunday at midnight” but I usually mean “11:59pm Sunday plus one minute”. It’s a simple misinterpretation tbh
I would usually assume it would be the midnight from Sunday to Monday as well (with it being a weekend and all), but then the information us Europeans are getting doesn’t make sense. Because if it ends at 7:00 AM UTC on Sunday the 4th (which is 9 AM here) and we’re ahead of NA times, where does the extra day come from? Because it’s not as easy to mistake one day’s 7 AM for another as it is to mistake a much more vague ‘midnight’ for something else.