The triumph took them past the previous record of 14 wins by English top-flight clubs in all competitions, jointly held by the Preston side of 1891-92 and Arsenal in 1987.
“The record will be broken for sure, because sports is like this, but it means a lot, to do what we have done in the winter time and Christmas time is quite remarkable.
“It is the toughest time, but what is important is the way we are still playing with our consistency.
“We have an incredible week ahead of us and we will approach it game by game.”
Defender Ruben Dias and midfielder Fernandinho did not travel to Wales, but Guardiola hopes the pair will recover in time for Tottenham’s Premier League visit on Saturday.
“Ruben had a fever and still has a problem with his stomach,” Guardiola said. “That’s why he was not able to train and today we travelled.
“Fernandinho had some niggles in the quad and he was not able to play, but we played a strong side. I know we were comfortable with the ball, but every time they break our pressing they create chances.
“They’re a really strong team, but we’re in the next round so I’m very pleased.”