This thing you explained happened during the just conclude WAFCON were Nigeria was losing to Morocco 2 - 0 first half. It was like Nigeria side would not be able to win against the Moroccan players but all of a sudden the game changed and Nigeria won the match just like that.
I believe many gamblers actually placed a bet on Nigeria to win and the way the match started, many people lost hope because in such a situation, it could be very difficult to equalise not to talk of winning the match but it was a different ball game altogether Nigeria did not only equalised, but the Falcons won the match. For those who held on to their bet believing that Nigeria would win, won their bet but for those who couldn't bear the risk could not stand to bear the pain of not being patient till the end of the match lost their bet.
Based on statistics and the performance of Nigeria in their previous games many people had to choose them as favourites not only that but including the record the Falcons had kept in their past finals, all those are what many folks considered before picking them to win that particular match. Well those who believed in Nigeria and have seen them attempt several comebacks in the same tournament would definitely risk on them even though they were down on two goals, whereas those who had already better on the stronger team and share similar believe on their favourites strongly held on to their instincts till the game turned around in their favour, it's not an illusion but they held on to what they ought was the best and were lucky afterall.
The Falcons had a clean record from the onset of the WAFCON and other previous games they had played in the past and there is no doubt on their performance hence gamblers trusted them to win by betting in their favour and with such records, it would be very difficulty to convince person that they would not clcinch the trophy when looking at the performance from the beginning of the finals. Hard supporters just like you said will stand firm because they know the Falcons would equalise and maybe the match would end in a penalty shootout and also those who bet against them too would have same opposite thought vice versa as the case may be. In situations as this, strong supporters and fan base never give up and most times,it turns out to favour them alot just like the magic that happened the just concluded WAFCON competition.