People say things.
The Kings are currently allowing opponents to shoot .386, the worst in the league this season. However, there are 21 teams in NBA history that have allowed opponents to shoot better than the Kings this year, led by the '10-'11 Cavaliers (.411). It is notable that the '09-'10 Kings are second on that list at .406.
We are, however, allowing the most opponent 3PTM per game in NBA history. However, 16 of the top 20 teams in 3PTM allowed are this year, and the other 4 of the top 20 were last year. This is part of a general trend. The league average 3PTM this year is 10.5 per game - which means that the league 3PTM ALLOWED is also 10.5 per game. Again, there are exactly four teams in NBA history that have allowed at least 10.5 3PTM per game outside of this season, and they were all last season. Frankly, there's been a revolution in three-pointers - over the last 10 years, the average 3PTM per game has gone 6.4, 6.5, 6.4, 7.2, 7.7, 7.8, 8.5, 9.7, 10.5. Three pointers have shot up in the last 3 years particularly, because teams have finally started to understand that scoring more points per possession wins games.
So that's where they're getting their numbers - by saying that in a season where the league has shot and made more threes than ever before, the Kings happen to be the worst team this year at defending it. However, if you were to normalize 3PTM for league 3PTA, I have no doubt this year's Kings wouldn't crack the top ten.