I find multiaccounting is a good way to test new maps or mods, so I don't think that it should be banned.
it isn't against the rules to do that like a 1v1 just to test how maps turn out on distribution i use it for as well and then just VTE with both accounts so i'm not getting anything out of it at all.
If you play a normal game which is the case in this scenario and you play on different teams it's against the rules since you get an unfair advantage with knowledge about both of the teams in this case although in this specific game it was Light Fog so the advantage isn't too big but still you should not do this.