Was what just happened to me a virus, or....?

I'm not sure where else to post this, but if anyone wants to redirect me, that would be great.

So I was browsing r/fiftyfifty on an app called "iAlien for Reddit". I had clicked on a few posts when I got a pop-up that claimed I had been accused of looking at illegal porn and listed a few different kinds. It also listed some legal stuff. I deleted the app immediately. I know I wasn't looking at anything illegal (at least I don't think I did, I may have clicked something I didn't know about), but it still terrified me nonetheless.

Any help?