IMO strong vibes of urban legend and gossip.
As to Rennenkampf and Samsonov hating one another and "not working together well" - I'm fairly certain there were such examples in other armies of the period (there are many examples from the French Revolutionary and Napoleonic Wars era). I'd say that such a problem exists since 2000BC or so
Not in that case.He was polish aristocrat close to russian inner circles ,and since 1915 lived in France,so he saw how politics was made.French start beliving him when in 1915 he gave them memorando stating that russian would never gain again territories lost to germans,Italy would be useless,England would fight using France - but they eventually would win.Becouse all that was true,they start listening to him.