Two things - Liverpool's goals were ridiculously good. When's the last time Man City got blown off the pitch? Liverpool's energy levels are too much for most teams.
Secondly, even though 9 points is a huge gap, its really not insurmountable - its the start of November. Leicester, Chelsea and Man City are difficult opponents, on their day Manchester United and Arsenal could take points off them, and Everton could too depending on how seriously Everton take the derby. There's no way Liverpool play the rest of the way winning them all or dropping very few points. It took a super human effort last year to win all those games at the end.