This is all because of social media. Companies have been warning and reprimanding employees for slip ups like this way before social media, way before the internet went mainstream. My wife worked at Coca-Cola during the summers when she was in college and she was given a stern warning from someone in management when they caught her drinking a Pepsi owned product. It was a brand of juice that she didn't even know was owned by Pepsi. She didn't even know that Pepsi or Coke owned juice companies.
This Huawei/iPhone tweet was more blatant as it clearly promotes Twitter for iPhone. I can understand management's reaction, but I think they shouldn't have aired the punishments publicly. It does make them look bad.
A stern warning would have been exactly the right response to this, certainly not a pay cut. I'd be appalled if a company I worked for did this to anyone over a mistake, even a much graver one.