Acquiring an app from a Chinese company and slapping the Microsoft branding on it without doing some sort of vetting would be absurd.

What’s absurd is thinking Microsoft doesn’t have anyone who can read source code.

How is it different from acquiring a US app?

According with the new cold war narrative, in this case we have an very evil code that spy people all the time. Forgetting that last time I checked, companies proven by leaked documents to really spy and pass information to the government was Microsoft, Instagram, Facebook and Google.