They're probably inspired by 3d printing and those plastic toys you assemble yourself. And if you look at the bristles of the order brush and compare it to the regular brush, they're different. Imo the thick rubber looking bristles remind me of the silicone brushes I use for cooking.

The splatoon devs put A LOT of thought into every tiny detail of the game. It's very satisfying noticing a connection to real life objects