At 0.18 they're still walking out of the tunnel....oh I see, you changed the video...
From this angle, the keeper has run out, completely missed the ball and cleaned up the attacker. This isn't a case of 'they both ran into each other', it's clearly the keeper's fault.
Referee was also being lazy - we can see at the start that he is inexplicably jogging to the right touch line instead of recognising there's an attack and moving upfield with haste. As such,at the time of the foul he's directly upfield and quite some distance away, when really he should be, I'd say, a bit outside the PA to the left of the arc, giving him a view through the ball to the AR.
I'm guessing, but I can't help but wonder if it's a bit of 'I don't want to give a penalty early in the match' and 'something happened with the keeper. Must have been a foul against the keeper'. Given the laziness evident in this moment, that seems plausible.
of course, with wireless comms, there should be no reason to guess. For all we know the AR could also have had an input.