If they went guessing he was flying from Toronto then they were either super lucky the gates were the same or caught on real quick he didn't take that flightIncheon is a pain in the butt for arrivals even if you know what country the person is flying from!
But yeah theres a bunch of ways people would be tipped off that he departed. And pm if you have a vague idea of what day anyone is likely to fly/arrive and where they are flying from (even better, preferred airlines) it's fairly easy to guess flights. So, unless he's snuck out of Canada and is taking a creative route to Helsinki, it's fair to assume some fans will form a greeting party XD
They found out he flew from Sendai, apparently someone saw him there. Once they knew, it was not that difficult to figure which gate because there is only 1 flight from Sendai to Seoul with ANA. But I doubt something like what happened at SK or China would happen elsewhere. It did not happen at GPF for few years before or at Boston last year. I only noticed people greeting him at the airport to happen during CoC, 2015 worlds and 4CC. Others are after competition when he returned to Japan.
Some fans waited at the lobby of the official hotel though, which is why you would not see Yuzuru hanging out at the lobby of the official hotel much anymore.
: 
