had the same on my outdoor plant i was worried too , but i figured it's down to two things. Obviously genes will do it, pistils will go brown sometimes quicker sometimes never. The second thing is when you're outdoors you basically can't explain everything, like why this or that leaf got damaged or this or that flower got damaged. Looks like a bit of minor wind (+sun!) burn to me. Is it something to worry about , not at all unless it spreads and the plant starts showing other symptoms. Growing is nerve wreaking, simple as that ! 🚀