Hair pulled from wearing a hat. Could this have damaged my results?

At one month post-transplant, the grafts should be well-secured in your scalp. It's unlikely that an incident like your brother pulling your hat off caused permanent damage to your hair transplant results. After the first 10-14 days, the grafts are typically rooted and less prone to being dislodged. What you likely experienced was hair shedding, which is common in the early stages of hair transplant recovery, especially during the first few months as the new hair follicles adjust.
The empty spots you’re seeing at 8 months could be due to a variety of factors, such as uneven growth or slower regrowth in certain areas. Keep in mind that the full results of a hair transplant can take up to 12 months or more to be fully visible, and some areas might fill in later than others.
While the hat incident may have caused some immediate discomfort or shedding, it’s unlikely to have caused any long-term damage. I’d recommend giving it a bit more time to see how the growth progresses and, if necessary, you can explore additional treatments or touch-ups later on.