They just worded it wrong, really... It should say it's 52.9% of what it was in 2013, meaning it is a 47.1% drop.
But linking to data for 5 months and then only using the 4 you want to use to skew numbers seems pretty ridiculous to me.
And then in the same page there's data for drug/narcotics violations which isn't even mentioned because it is going up (21% more) even though there are supposedly plummeting marijuana convictions. Also they stated that the crime rate in Denver is going down, yet the data shows the exact opposite.
Whole article seems like cherrypicking at its finest.