Their response does not make sense: [the police's] absence of evidence [for your complaint] does not constitute evidence of absence [of what you claim happened]

Their response does not make sense: [the police's] absence of evidence [for your complaint] does not constitute evidence of absence [of what you claim happened], so this absence of evidence does not form a basis for charging you with a false complaint (unless they find actual evidence that whatever your complaint claimed did not happen)