Yes, they would have been very wrong. They would have been racist in their outlook. It's ridiculous that we are living in almost 2025 and we still judge by skin colour. If you're born in a country and you have that country's nationality, you should have exactly the same say as anyone else and be exactly the same level of national of that country as anyone else in the same position. So it doesn't matter about 'white English children'. Instead we should be looking at addressing the roots of the inequalities of opportunities that different groups face, and deal with them.
The man who attacked the Magdeburg market is clearly someone with major issues - around identity, race, culture, politics and possibly also mental health, though that remains to be seen. It's deeply ironic and sad that the AfD are now demonstrating, given that by all accounts he agreed with them.