I have a reactive stomach and had fairly bad GERD before my Nissen. I couldn't then, and can't now drink much/or any coffee. Tea has never, and still never bothers my stomach. I drink regular black tea, and it does not bother me. Why? No idea. I do drink decaf black tea often, but I don't really have a problem with caffeinated, either.
I think even at its strongest, tea isn't as potent as coffee. Plus you can brew tea very light and it still tastes good. Coffee is far more acidic and aggressive on the stomach.
GERD triggers are very individual. What bothers one person, doesn't bother another.
One other thing I'll mention. Caffeine has an effect on the LES and from what I've heard weakens it. Because of that, it can increase GERD symptoms. My PCP wanted me to stay completely away from even decaf tea and coffee, and preferred I drink herbal teas for that reason. I don't enjoy herbal tea, and stuck with weaker brewed regular decaf tea, and never had an ounce of trouble.
Good luck with your quest for answers!