I mention this in the latest JSR but I don't think I talked about it on twitter. During launch of the CZ-5B/Tianhe, about 6 minutes after Tianhe and the CZ-5B separated they both came close to the ISS - under 300 km, which given uncertainties in trajectory is a tad alarming

To pass SO close to ISS is really unlikely, requiring fine timing, and does raise the possibility it was done deliberately as some kind of gesture. I gather the ISS partners were NOT warned it would do this.

I would welcome calculations by others using the relevant TLEs to confirm my conclusions here - my code is not the most accurate for this sort of thing.