I think the numbers are wrong.
Let's do the math again
Tyreke played 58 games so far.
So, in order to average 20/5/5 he must have :
58*20 = 1160 pts
58*5 = 290 reb
58*5 = 290 ast
According to his nba.com player page, he currently has 1180/281/315
So his +/- is :
1180-1160 =
+20 pts
281 - 290 =
-9 reb
315 - 290 =
+25 ast