It was a night to forget for Premier League champions-elect City, who were ambushed by a relentless Liverpool side in the opening leg of their mouth-watering quarter-final tie on Wednesday.
City's underwhelming performance, which saw Guardiola's men fail to register a shot on target, came after the bus carrying the visitors from Manchester was hit with projectiles, including bottles and fireworks as it made its way to the Merseyside stadium.
Liverpool and Jurgen Klopp apologised to City before kick-off but Guardiola was less than impressed following the final whistle, given there was prior knowledge of fans planning to follow the vehicle.
"Yesterday you explained about that, it is going to happen, and it happened. I didn't expect that. I am new here," Guardiola said.
"Normally when the police know that is going to happen, they try to avoid it happening. I did not expect that from the Liverpool side, from the people.
"One year ago, something happened in Dortmund. We come here to play football and I don't understand this kind of situation.
"The bus is destroyed. I didn't expect that a club as prestigious as Liverpool would do these kind of things. Of course, it is not Liverpool, it is the people – it was not only one, only two, only three. Hopefully it doesn't happen again."
City midfielder Kevin De Bruyne, however, played down the incident, adding: "It was ok. I don't mind supporters doing that. I've had it before for my team. I think it's a nice feeling.
"Breaking windows is probably not done. But who am I to say something? I'm ok with it, as long as nobody's hurt I'm fine. No [it didn't affect the players], it doesn't change anything. As long as you keep the violence down there's nothing wrong with it.