The Drengin may not care what Ideology you are. I'm still learning how diplo works but I know I believe they value each offense differently. Altaria HATES you if you are not the same ideology as them and the Kyrnn are worse. The Kyrnn are usually the first to declare war on me.
The Krynn are super aggro in general. They're usually the first to declare war on me, and I'm Malevolent just like them. Then again, I usually don't have my army ready by the time I meet them. If my army is ready, then the Altarians will certainly declare war on me first.
But yeah, not all races care about your ideology. Krynn and Altarians are super anal about it, but Drengin don't seem to care one way or another. Good, evil, they plan to eat you all the same. Most races do kinda care, and if they do, your ideology doesn't have to oppose theirs, it just has to be different than theirs.
Think of it this way: Benevolent races care for their people to such a degree that they impose rules and regulations that stifle profit, and give everyone miles and miles of red tape in order to do any kind of work with them. However, they make life extremely cushy and enticing. Dealing with these people can be a pain because all your best and brightest end up leaving your civilization for theirs, so you end up with a shortage of skilled workers. And then comes the preaching. Their way of doing things might not even be the best way of doing things, it might only even work on paper, but damn if it isn't the most popular with The People.
That is how a Pragmatic civ can come to dislike a Benevolent civ.
Malevolence is the opposite. They suppress freedom in the name of border security, profit, efficiency, and order. They are extreme nationalists who believe that might makes right, and because their people are so prideful of their might, they can be extremely dangerous neighbors. That's expected of them.
Pragmatic civs wouldn't tolerate them just because they aren't a polar opposite - they're brutal dictators!
So this is not a bug. You're Benevolent, but Terrans are Pragmatic, so they dislike you. Drengin don't care about ideology, so they tolerate you. You can check to see in your game with the Report button if you want to double check.