I don't condone hoarding, especially if what is hoarded will be discarded or if it for later re-sale at a profit. But I bet we are all buying a few more days ahead than we normally do - I certainly am because 2 or 3 mini-shopping trips a week is more of a risk than 1. And please don't judge me because I've got 24 eggs and 3 packs of butter in my trolley - I have 2 neighbours who can't get out. Other people you see in shops might be buying for others, have a large family, or just be unable to get to the shops regularly.
While I don't condone hoarding I can understand it. We all behave rationally, but we have all had different experiences and 'rational' differs from person to person. My father saw great deprivation in Italy (Bomber pilot, 81 ops) and the UK during and post war. His father was killed in 1917 so he said they never had enough food at home when he was young. When I was growing up in the 50's and 60's he always kept a few tins in the cupboard - beans and spam I think - and a productive garden. I never asked, but his 'rational' was probably that he never wanted his family to go hungry. I worked in HR on Merseyside in the 80s, some of the union reps told me about their experience when young, fathers doing casual work on the docks and bakeries and in lean weeks they went hungry. That's why they didn't trust, or even hated, the bosses. There are lots of stories like that - then and now. I am a school governor and we have children coming to school hungry, in 2020 in what is a rich nation. What will their behaviour be if one day they can afford to hoard a little?
We have had inconveniences, sugar shortage of '74 is an example and it wasn't a real shortage even then. Many of us, including me, have never lived through proper unrelenting hardship. I would be distraught if my children when young had said "Dad I'm hungry", really meaning it not just whingeing, and I could do nothing about it.
Maybe your friend was regularly sent to bed without food as a punishment as a child, maybe long ago his family went hungry for some reason, maybe he feels a strong need to be the provider (we no longer leave our caves and return 3 days later with a dead elk on our shoulder, we come home from Tesco with a boot full of goodies). Maybe he sees himself as a rescuer - when the chips are down he has the resources to provide for relatives. You will never know and can never ask, you may not approve but maybe you can understand that what he thinks is 'rational' may not be greed but something else altogether.
What if he had never told you, never proudly shown you his stockroom? Maybe you have other friends who have stores of this and that but haven't told you, would you be just as angry with them if you found out? Was telling you the mistake? I'm not supporting hoarding for the sake of it, but we should all try to understand why we act differently from one another.
We might all lose friends - or they us - to the virus, making peace might be the best thing we can do right now. When you are on a ventilator you can't speak. I'm not saying that to be gloomy, just realistic. Maybe we should all hoard as much goodwill as we can, just in case. I wasn't a part of the conversation you had with him, so mustn't judge and may have done exactly what you did, but maybe you can build a bridge back one day soon.