ANYTHING IS POSSIBLE with a mess of old wiring. But what I suspect you had was:
- All whites were neutrals and all connected together, which is generally correct.
- Ground (bare) wires connected to each other and to various devices as appropriate.
- Black hot and/or switched hot wires, and possibly red wires as well (depending on whether the "3 wire Romex" meant black/red/white + bare ground (the usual meaning of "3 wire Romex") or black/white/bare ground (three physical wires in each cable, including ground) connected to various switches and receptacles.
The result of all that is indeed that the receptacle did not have neutral - i.e., "open neutral". If that's the case then all you needed to do was to connect neutral of the receptacle to the bundle of white neutral wires. But that is only a guess at the moment.
Ordinary (not: smart, WiFi, motion sensor, timer, etc.) switches do NOT use neutral. They might connect to a white wire, depending on configuration (old switch loops, some 3-way switches). So connecting white to the switches was a bad move, and at some point you ended up with a short circuit. Fortunately, your breaker works!
If you have "before" pictures then upload them. It may be possible to figure this out relatively easily. If you don't have those pictures then this is going to be a slow process of identifying:
- Which cable is bringing in power from the panel
- Which cable(s), if any, is going to feed other things
- Which cables connect to switched devices (lights, fans, etc.)
- Which cable is going to the "open neutral" receptacle
Note also that the 3-light testers are what Harper calls the Magic 8-Ball. Because it gives a seemingly mysterious answer that may or may not have anything to do with reality. They are actually quite simple devices that work reasonably well with modern wiring. But when there are strange problems you can get strange results. The truth is that "open neutral" tells us that:
- There is no current flowing between hot and neutral
- There is current flowing between hot and ground
- There is no current flowing between ground and neutral
That can mean the neutral wire is not connected. It can also mean some other things. With messed up wiring it takes a little digging sometimes to figure out what is really going on.
A non-contact voltage tester and a multimeter are very useful tools here. A 3-light receptacle tester only tests receptacles and in a very limited way.