Many homeowner associations make up “rules” as they go. If it is not in the deed restrictions, the HOA is probably acting beyond its legal authority.
My sister is in a HOA. They actually told her she would have to pull up all of her flowers, as they were the wrong color and she did not receive permission to plant. One short letter from an attorney threatening legal action was sufficient to stop that stupidity.
Sounds like the HOA rules allow large vehicles in the driveway and smaller pickup trucks don’t qualify. It’s probably not a ‘’class’’ type of rule. It’s still asinine but that’s what you get when you volunteer for a whole other layer of government. I learned the hard way it’s not a good idea to live somewhere my neighbors have a say on what color I can paint my house or where I can park my cars on my own property.