As the co-commentator said when asked when Sigurdsson would have even looked up for that:
The start of the half and Hajduk were in possession, it was safe to assume the keeper was well off his line as most are.
His positioning was common and you can't judge him on that really, it's just one of them things.
It's how long he took to get back, what arm and the angle he threw it up at.
Does he seem to give up thinking it's sailing over?
I wouldn't be surprised to see most keepers let in something like that because it just doesnt come up in the percentage drills they go through in training.