I know the whole movement that got Trump elected started from this but at that time it was as far as I know not called alt-right (because I remember the thread on 4chan were they actually made it up).

Yes, the division between groups (pro/anti) created while gamergate was going on were about the same. On one side people calling for social justice on the other side the people that in a way are against social justice + the ones that did not want to choose a side.

At the beginning gamergate was just about ethics in journalism (mostly in gaming).