Guardiola was asked about Raheem Sterling refusing to admit he tripped over the grass when the side were awarded a penalty against Shakhtar Donetsk on Wednesday night.
The Spanish coach said after the game: "He [Sterling] could do that [admit the mistake].
"But last season Liverpool… Milner could say that the pass to the second goal in the 44th minute it was a legal goal.
"But Mateu Lahoz didn't want to concede that goal, so that's why it happened, but he [Sterling] could do that, yes.
"We don't like to score a goal in that situation but [Sterling] didn't realise.
"The referee at the end realised. The Spanish referee Mateu Lahoz, he realised, he didn't want to concede.
"But in that situation [Sterling] didn't realise because he wanted to chip, caught the grass, goes down, it's not a penalty."