Reddit's userbase grew very quickly after Digg drastically changed, aka 'collapsed', Reddit for a while also engaged in sockpuppeting posts to generate fake traffic to create the illusion of a userbase before it really took off.

4chan, in comparison, has always been organic from day 1.

But many OPs of 4chan threads sockpuppet their own threads in order to make their thread gain traction.

It's not made by the website owner so it still counts as organic

Wasn't founded until 2005?

You could make a case for slashdot or wikipedia or google, but IMO all have changed substantially in the last decade.