Would love to know anything more about that reaction.
They have a website version but it's a paid offering, with it being part of a subscription now. It used to be a one-off purchase. Regardless, I haven't used it before.
Obviously I can't know what you have tried before, but I'd highly recommend Pocket Casts. I've been using this since at least 2014 (looking at a support chain that I had opened) and can't imagine losing the features they've got. It's shifted owners a few times and their mobile apps are now open source should you be interested in that.
It's not a bug, it's a feature. Look under settings for volume button comment navigation.
I'd tend to agree that it's not an expected default, but it's easy to disable.
You can use old.reddit.com to bypass that, at least for now.