That’s how neurons work, yes. But you can’t reduce a “decision” down to a single neuron. It depends what you mean by decision really. Do you mean “the smallest thing that can affect something else”, in which case, yes, neurons are the smallest unit (it seems) of brain function. But not consciously so.
Or do you mean the collective input that goes into the brain generating an output? In which case, the brain appears to function more with swarms of neurons firing together. You won’t find any examples of a single neuron affecting, say, the choice of going to the cinema. We don’t know the brain in enough detail for that, nor does it seem possible for it to work that way (neurons die and are replaced but our behaviour and decisions seems far more stable).
Or do you mean the conscious experience of making a decision (free choice)? Which is a different thing again. The mechanics of the brain operating input and output and the conscious experience of it are not the same thing. They may be generated by distinct but overlapping parts of the brain. Often in step but not always. Conscious choice can’t have elements of it reduced to single neurons, brain experiments seem to frustrated any attempt to turn up evidence for that.
Whatever it is we colloquially mean by making a conscious decision about something doesn’t exist on the neuron level. It exists on the millions of neurons acting simultaneously level.