I thought all 3 defenders had a hand in conceding that. I mean, with 3 CH's you shouldn't be conceding a long ball from the keeper for a start. Tosin should have done better with the header, Hegazi did the right thing dropping back when he realising he wouldn't get there, but Bartley should have been dropping to help Hegazi out rather than watch him in a 1v1. Hegazi should also have done better there.
First error for the goal is Adarabioyo misjudging the clearance and getting caught underneath the ball. That shouldn't be happening.
Second error (and the most crucial) is Mears not reading the situation and not following his runner. There was no other danger, Mears has to track that run.
Hegazi then is left in the proverbial. Either he goes for the challenge which is 40-60 and risk a foul and very possibly a red card or he drops off and at least gives the attacker another obstacle. I think he does the right thing but the forward does very well and changes direction and with Hegazi having to react to the change of direction I'm not sure he could've done much more.
Looking at Sam Johnstone's positioning, I think he should be taking another step to his left. The forward is always likely to shoot into the keeper's left corner from there given the direction he's running in. If the forward shoots across himself then fair play, hands up it's an outstanding finish. Could / would Johnstone have saved the shot had he been another yard to his left? Probably not, the guy hits the shot too well so although I think his positioning could've been better I don't blame Johnstone for the goal.
Blame for me lies with Adarabioyo and Mears.