Sort of, not exactly how I remember it. 8ch appeared because 4chan’s boards are dedicated to certain topics and some subjects fell through the gaps between boards. I remember 8ch getting popular when incessant gamergate spam was banned from /v/. 8ch also has a “popular” leftypol board which is the left wing counterpart to 4chan’s pol (there’s no good place on 4chan to discuss Bernie Sanders, for example, without getting mobbed). Raids were also banned from 4chan and some other things which brought unwanted attention to the site, I think those people also went to 8ch. A final group of people left to 8ch when Moot (the person who used to run 4chan) scrambled /pol/ for a week (?), making the topic board unusable for regulars. Any other growth of 8ch is beyond my knowledge of the site.

8ch gained popularity because gamergate discussions were censored on 4chan.