I'm pretty sure it is. Shiloh, Shadow, Georgie, Suzi, Sarah -breathes in- Reggie, Riddle, Admiral, Marge, Tina, Zebra and Rose all had ammonia burns, plus other bettas I've had too, including a newbie, LaLa and Misteltoe have minor ammonia burns.
A 0.5 can get so much more ammonia in it because of the small space. That and cold water can lower the immune system, making him susceptible to diseases and parasites. I clean my 1 gallons every other day, unless they need every day cleaning via the burned ones, rotted ones, ich ones.