They said it to show the Zentorno is the direct competition of the Adder...
Even though the Entity is closer to the Adder's price and technically should be faster based on the game files...
But yeah, to put it as simply as possible, the Adder and the Zentorno are direct competitors.
It was also a way for R* to troll Adder owners by releasing a somewhat cheaper car, with actual visual mod options, that's basically the same speed but with improved handling and acceleration.
And yes, the Adder gets a bad rap because of the people that were notorious for driving them but more so the paintjobs they had on them, the whole "Chradder" sh*t.
The Adder is a very good looking car when treated with some dignity. I own two Adders, one on each character, one is Classic Black with Blaze Red pearl and chrome secondary, the second is classic black with no pearl and Formula Red secondary. They both look sleek and stylish and I can't say anyone's ever given me sh*t for them.
For the record, I own 8 supercars total, 4 on each character and they're all the "Big 4" of the class; Adder, Entity XF, Turismo R, and Zentorno.