Hey, buddy! ππ
It's 100% due to a concentrated beam of sunlight! The light could have passed through glass (bottle, cup, window) and, concentrating into a hot beam, lightly touched the edge of your plant! Even the bleaching nearby means it's definitely a beam of light that passed through something like a prism. π There's nothing to worry about, but it's better to watch the movement of bright rays around the plant during sunny days and clear weather! π
This is light burn - in other words.
Good luck, buddy! βπ