I think they are designed for uses other than cycling.
Bicycle parking?
But they’re sat at the side of the bank ,so what difference is camo gear going to make ( unless I’m underestimating the eyesight of your average fish )?
We have loads of “Sport fishing” round our way, lots of dour looking middle-aged men escaping their (clearly horrible) wives with a wheelbarrow full of “Gear” sat by a flooded gravel pit.
All of it is either Olive green or DPM, I think it basically comes down to the cheapest, most plentiful source for outdoor kit bing a surplus stores.
I much prefer to think they are trying to outwit fish, or be absolutely certain their missus can’t find them…
Having said that they may well be sporting the OP’s linked outfit underneath, could “Angling” be the new “Cottaging”?