Why was my cat eating grass?

Yes, of course it is normal.
He is not really eating it, he just swallows it to clean his stomach from the fur that got into him while cleaning his pelt.
Dont be afraid if he starts to cough after a while, this is how it goes.
Or so ive seen my cats doing it.

This is completly normal cats also tend to
do this when they feel like they need greens
its strange but normal :3.

It's completely normal tahat a cute eats grass that's the cleaning out there systems, getting healthier, and they might be sick.So it might be ne of these reasons

when they eat grass that means there stomach been heating.

I'm not sure but i think that your cat might be playing with it like strings