I think the same, i've been deploying containers or things that look like today's containers for the past 12 years, i even did a tool that manages containers with lxc that really look like docker, but 3 years before.
There were many solutions very similar to Docker, but you have to agree that they made some essential things the right way - UnionFS (e.g. OverlayFS), standardized way of building containers (Dockerfiles) and the right timing.