Yes that's part of the reason it could be partly racism. The government knows the affluent in London will flee (as they have been doing). Still today, affluent people are more likely to be white. Not exclusively so of course. Which means many left behind in London will be non white including many migrants. Others left behind are elderly or disabled. All groups possibly seen as costly to the government. The government failing to act to mitigate the spread could be down to seeing these people's lives as less valuable. It's a mark of a civilised society how we treat the most vulnerable.
Yes those leaving London will spread it to other parts of the country but our government seems to act on short-term thinking.
Of course it's quite possibly nothing to do with racism or contempt for the vulnerable. It could well simply be complete and utter incompetence. Either way it's not good enough.