From the URL, the article is talking about a list of the 50 most violent cities. Presumably this list is updated annually, with cities moving on and off the list from year to year as they get more or less dangerous. The further implication is that the violence being tabulated is for the current year (or the most recent year for which statistics are available).
The is the first year that Los Cabos, Mexico, is anywhere on the list, meaning that last year (and all other years previously) it was not one of the 50 most violent cities. That is, in years prior to this one, it was at worst the 51st most violent city.
The article is mentioning this to emphasize a very sudden and large increase in violence. Last year, Los Cabos was safer than at least the 50 cities that made last year's list. This year, violence is so bad there that it jumped ahead of all 50 of those cities all the way to the most violent city spot.