I was not criticizing your vegan diet. Your friend's experience is just that, his experience. His next concussion may take him much longer to recover. Nobody can say.

A simple vitamin a day with 2 glasses of water is quite minimalistic, especially for someone who consumes 4 beers in an evening.

I bet you also changed other behaviors when you started your vegan diet.

It is likely that your youth has more to do with your recovery than your diet. Plus, an impact to the back of the head without involving the upper cervical vertebra is in many cases the least injurious to the brain. There are less whiplash like forces. Side impacts with/and rotational forces do the most damage.

If you had been a girl at the low point of her progesterone cycle, you may have suffered more damage. Guys have a safety net amount of progesterone flowing through their system constantly that is neuro-protective.

Some researchers think that having some alcohol in the brain during an impact may reduce some injury by slowing the processes of the brain. The research shows that more than a single serving per day of alcohol has a negative impact on recovery.

It appears that you likely suffered a very mild concussion with more of an impact to your skull causing your head aches. But, no one will ever know. Even the best concussion specialists struggle to diagnose the intensity of a concussion at the lower end of the concussion spectrum.