Its silly since truly its neither. But I grew up with the expression of
learning something by osmosis
to mean gathering into your brain as if pulling it in from the aether. And this expression is definitely still in use.
I heard this expression way before I had any idea what either meant. By the time I got through High School science I had definitely had these two defined. From a random google site, comes this succinct definition:
Diffusion and osmosis are related concepts, which involve movement of materials from areas of high concentration to areas of low concentration.
Diffusion involves movement of any chemical from one place to another; osmosis refers to movement of water across a membrane.
Only water can undergo osmosis.
Years later I ran into the importance of using hypothesis instead of thesis, to describe an idea that one had that needed proving. And yet noone ever seems to complain about learning by osmosis.
Okay, you probably don't REALLY learn by diffusion as though knowledge was a chemical moving from one brain to another, or from a book to a brain, or a computer screen to a brain. But you certainly don't learn by the movement of water across a membrane. I'm pretty sure that knowledge is not water. But I am not as certain that knowledge or memes are not some form of chemical. So.
I learned it by diffusion. Try it out.