After my earlier post, also on WeChat, as well as postings by others, I could tentatively conclude: there might be indeed some isolated incidents but it is not a big trend. Well, a bit reassuring. It there were more, for sure some people would have come forward, or?
See here some of the postings I found, slightly edited but leaving the text as it is, just putting it all together:

quote
Don’t want to scare anyone. But please watch out your back. There is a group of Chinese guys attacking foreigners that go out with Chinese girls or guys. They always attack with baseball bats and iron loads. They already attacked in village, around heavens and wudaokou, the street of Blcu, houhai and nanluguxiang.They usually use a grey Bmw but pay attention to other cars too. Usually if they are driving and see foreigners and Chinese together they get out of the car and start yelling Chinese girls belong to Chinese guys. This is the info that I got from victims that contacted me yesterday. They attack foreigners: white, blacks, Hispanic
Please share and if you know any case please tell them to report to the police and write an article at the magazines that are read by expats. …
Call the police or go to the police station to report the situation. They already know this but did not identify them.
Heard that a group of 4 had baseball bats yesterday @ wudaokou and that this group is looking only for foreigners. So anyone knows if this is true or not?? Because my female friend also got attacked by by a group of guys in Uibe area.
All the cases happened with foreigner guys walking with Chinese or Mongolian girls
unquote

And this is the only published article I could find:
http://www.theworldofchinese.com/2014/12/foreign-victim-of-alleged-attack-says-stay-polite/

Well, if anybody has comments, let me know. And always better to be careful. Anyway I think Beijing is safer than many parts of Belgium where unfriendly foreigners are aggressive towards … Belgians. Or, the world upside down.