AITA for saying that an Indian girl was cheating at Scrabble?

So my (M23) GF (F23) has this Indian friend (F18) called "Priya". Priya came to my English speaking country (relevant later) a year back to study. My girlfriend absolutely adores her and Priya soon became my GFs "best friend". I'm doing English literature and she's in science (also relevant).

Recently, she invited my GF and I to her place (fluid restrictions here), and had made a bunch of Indian food for us, got some wine. I ate well, the food was good and was having a good time. My GF had apparently bought Priya a scrabble set because Priya had mentioned she loved the game, so GF suggested we all played scrabble.

I was really excited because I knew I'd decimate them both easily. We play, and as the game progresses, it wasn't me who was leading but Priya. She was making these huge words like "maladies" and "ostensibly". I was pretty sure she was cheating.

She got up mid game to go to the bathroom and spent about 3 minutes there. I'm pretty sure she was googling words in there. So when she came out, I jokingly told her I knew she was cheating and she asked me what I was talking about.

I told her I know that she's cheating, and that it's impossible for someone who's literally lived only in India all the time to be so good at Scrabble and to have such an extensive English vocabulary.

She didn't say anything to defend herself but just laughed and told me she wasn't cheating and we eventually finished the game and went home.

My GF however was extremely upset with me and told me I embarrassed her. When I told her I was being honest, and that there's no way Priya could've beaten me without cheating, She told me I'm a racist and that she's reconsidering her relationship with me.

So AITA?