It's funny you say that, because while I was confused at first too, I found learning the mechanics on my own to be the most rewarding part of the experience!
Like "ohhh the fish have interactions with each other in the inventory" or "ohhhh I shouldn't just hold left click the whole time while catching fish" and things like that.
I actually started off right-clicking while fishing, thinking I was "rotating the fish" or something to help catch it lol. So maybe they could tweak their instructional ui to somehow differentiate between fishing and inventory management.