Please tell me I'm not being too harsh

Long story short, I gentle parent, my brother and his wife do NOT.

So today I went on a hike with my brother, his wife, our mom, and their 4 year old son. I also had my husband and our 3 year old son with us. We asked both kids if they needed use the bathroom before we started hiking (because the trail had bathrooms before the actual hike) and my son said yes, so we took him to the bathroom. Their son (my nephew), said he didn't need to. So we went on and started hiking. And then 5 minutes into the hike, my nephew said he needed to go potty. Well, this did NOT sit well with my brother. He starts criticizing my poor nephew, saying things like "you've made daddy very upset, you said you didn't need to go potty before we started" "Daddy is NOT happy that you've decided to need the potty now" and "you know better. This is ridiculous, you should have gone potty before we left". So after talking down on my nephew for a few minutes, he finally decides to hike back down the hill with my nephew to go to the bathroom, but as they're hiking down the hill, away from us, I can still hear him berating his son and guilt tripping him (a FOUR YEAR OLD) for needing the bathroom now and not when we asked him. Yes, I get it's frustrating, but saying things like "this is ruining daddy's day" "this is ridiculous behavior and you should be ashamed" and "I don't have time this" is totally wrong, in my opinion. My son is 3 and just started potty training, but I would NEVER berate or demean him the way I was hearing my brother talk to his son. So tell me, am I being sensitive and ridiculous? Is it really not a big deal? Should I intervene? I just don't know. And when we were hiking DOWN the hill, after they had caught up to us, my nephew was asking to play video games on my brother's phone and my brother said "no, you've been bothering me and I told you if you keep asking, you wouldn't get to play. Daddy has given you many chances and you never learn, so you don't get video games. Daddy is disappointed." And at this point my nephew is in tears. I wanted to say something, but not even my sister in law said anything. No one said anything. This seems like normal discipline for them, so I didn't want to interject unless it was serious. I just don't know what to do about this whole situation. It seems like my brother is constantly guilt tripping and ranting to my four year old nephew about HIS feelings and HIS problems, not actually taking into consideration that my nephew (his son) is FOUR YEARS OLD, and doesn't understand how his daddy's emotions and feelings are his problem. It's ridiculous.