Robberies and property crimes are hugely underreported in official statistics because the first time you try to report one you realize that it makes a bad situation worse by wasting your time after the event. That is what they're talking about.
But you make a good point that a lackluster police response does lower the incidence of reporting crimes, effectively doctoring crime statistics. You'd have to evaluate whether this trend has increased or decreased relative to historical periods when factoring that into any comparison, though.
I have known people that had stolen things returned because the police found the items while investigating/arresting the thief for other crimes. It seems foolish to not bother with filing a report just because they aren't actively investigating every report they receive.
There is no "fact" saying how much crime is occurring, only a snapshot of how many reports were accepted and filed by the police.
Everything in shop is locked up, but crime is down!