If anything the whole thing was a bunch of mistakes from Poland: laughable mistake from Krychowiak (horrendous backpass...wtf was he trying to do?), then the oblivious polish defender thought there was no one around so he stopped running, a second later he saw Niang but it was too late, Szczesny realized his teammate was on another dimension so he started running but Niang got to the ball first...in conclusion, correct call from the ref, great reaction from Niang, crucial mistake by Poland for not being aware of what's happening on the pitch.
Yes, Poland made mistakes but the backpass probably wouldn't have happened if they knew there was a player there. He shouldn't have been waived on at such a time. He was off the pitch and out of play and was waived on whilst the ball was in the air and Poland were oblivious which gave Senegal a huge advantage which they unfairly capitalised on. The Senegal player was past the last defender so how are you meant to know about that? He essentially sneaked on.
https://twitter.com/TheAthleticSCCR/status/1009109694907076609
It tells you how many potential points you can get when you make your prediction.
I wouldn't give them too much credit. They've played shit teams and will probably go straight out in the group stage as they'll be facing likely Spain or Portugal. Lets see how they fare against Uruguay in their last game.