I cannot say that is not now the case, although I doubt it. It seems so unbelievable that one might think he was pulling your leg. 20 years ago there was a myth that police got paid more and got extra days off for making arrests. It not true but people still believed it. But I know times have changed so maybe it's true now.
As it is so easy to find people breaking the law I am surprised, if they really do get payments for making arrests, that any one is ever just cautioned.