[NorseViking]

Debka is quite a respectable truthful source in comparison to that you have linked.

[Widget Jr]

This is from a Russian source keeping track of Russian Mercenaries/PMCs and their causalities. The families of the dead and a lot of Russians are pretty mad at their government over this.

The Russians were not attacking U.S. forces; U.S forces were attacking ISIL. The U.S. was in contact with the Russian liaison at Deir-Ez-Zor who said there were no regular Russian military present. The liaison did not mention contractors, and the contractors were not told a attack was imminent.