Low voltage on circuit after breaker turned off - induced or backfed voltage?
It's hard to say without much more information about the circuits, but it is likely capacitive coupling between closely routed circuits. I've seen over 70 volts when testing a circuit that shared a conduit with a live circuit. Old meters didn't pick this up because they had relatively low internal impedance that allowed the voltage to drain quickly, my good digital has a very high impedance that does not shunt the voltage as fast as it builds up so I see the 70 volts(but is good for testing low amperage circuits). 
Capacitive coupling of this nature is very low total energy, kind of like a static charge it can't supply much current.



And be careful using cheapo meters on mains supplied circuits, they often have incorrect(12volt glass) fuses that will explode, arc, and burst into flames if you accidentally overload them or have the probes in the wrong holes.(eg. in the amp sockets when you think your testing volts, see https://youtu.be/R2ngaZwOgGM)
"Fluke T5-600" is great if you only do house wiring (simple single range so no good for fine electronics) won't break the bank, clever shape doesn't need 3 hands, and will last for decades.
I have a cheap $40 meter too but I only use it for current-limited devices.(small-battery power)