I found out my coworker was getting paid more than me and quietly stopped helping him

Few months ago one of my coworkers accidentally left a salary document open on his screen while we were working together. I wasnt trying to snoop, but his salary was literally right there and I saw the number before I could really look away. He makes about 20% more than me. We have basically the same job, started around the same time, and if anything he asks me for help more often than I ask him. I trained him on a bunch of stuff when he joined our team and I was usually the person he'd message when he didnt know how to do something. I was pissed, but I never told him I saw it and I never brought it up with our manager either. Instead I just stopped helping him. Not in an obvious way. If he asks me how to do something now I'll say I'm busy, send him the documentation, or tell him to ask our manager. If he sends me work to “quickly check” I dont fix his mistakes anymore. I just tell him what needs changing and let him do it himself. The funny thing is he has definitely noticed. A few weeks ago he asked if he'd done something to annoy me because I used to be way more helpful. I told him no, I've just been busy lately. Thats not really true. I know logically his salary isnt his fault. He probably negotiated better than I did, and honestly if somebody offered me more money I obviously wouldnt say no. But every time he asks me to explain something basic, all I can think is “you're getting paid more than me, figure it out.” I should probably be angry at the company, not him. Instead I've been quietly making his job harder while pretending nothing changed.