I did not touch any wiring in the room with the dimmer switch and ceiling fan. When I installed the ceiling light in the opposite room the wiring was already capped. 2 black and a neutral, 2 neutral, and a single hot black to the wall switch. The light fixture white was attached to the 2 neutral and the black to the hot black. Both box and light fixture grounds, were grounded. I say the switch loop provided power, because at one point I disconnected the neutral from the two black and lost power to the room with the ceiling fan. So, I reconnected it. Now when I turn on the dimmer switch the light in the opposite room comes home. Something is not right.

Your description of the wiring is a bit cryptic and difficult to follow. Are you saying that prior to installing the new ceiling light fixture there was a pre-wired box in the ceiling with no existing pre-existing fixture connected, and in that box was the following:

a) 2 blacks and one white connected together,
b) 2 whites connected together, and
c) a single black, which you believe comes from the wall switch.

It would seem that the white that is attached to the 2 blacks is hot, bringing power to the wall switch, and the single black is the switched power from that wall switch, which I gather is what yuo figured as well, right? Have you opened the wall switch to see the colors there to verify it's consistent with this? Do you have a tester to see how power comes into the wall switch? Given that the dimmer in the other room is controlling the fixture rather than the wall switch in the same room, could it be that these white and black leads are actualy connected to the dimmer switch in the other room, and not the wall switch in the room with the fixture? Have you opened up the dimmer switch to see how it's connected?