But did they?
No, they did not. The fault is 100% on the Polish side. Quoting from Wikipedia:
Both the Russian and Polish official investigations found no technical faults with the aircraft, and concluded that the crew failed to conduct the approach in a safe manner in the given weather conditions.
Earlier, Russia offered a Russian navigator but the Poles refused.
Why not...Poles, of course, always know better. Sounds familiar? Quoting:
Therefore, when "PULL UP" sounds, the crew is supposed to begin an immediate, maximum performance emergency climb (full power and angle of attack to the maximum permissible without stalling) and continue climbing until the warning stops.[23] However, the crew continued the descent
And to prevent "those evil lying Russians" comments:
Russia offered full cooperation to Polish prosecutors during the investigation.
Finally:
The MAK report found the "immediate cause" of the accident was the failure of the crew to make a timely decision to proceed to an alternate airport despite being warned multiple times of the poor weather conditions at Smolensk.
The incompetence was all Polish - including the ultimate act of packing all the big shots into one plane.