And the linesman did not have that view. Neither did the ref so they did the only thing they could do and played on.
Quite. It was impossible for the ref to keep up with the speed of the attack so neither of the officials saw it. Under those uncertain circumstances they had to let play proceed. It was too close a call. Officials are human and fallible. Given they don't have replays I'm surprised how many calls they get right. Having to run about, concentrate intensely and have eyes like a hawk. Tough job. These things happen all the time and you just have to hope they balance out over the season.
This certainly helps balance out a penalty claim or two.