Some philosophical systems described an active intellect whose emanation was said to account for human understanding. This is a historical philosophical model, not an undisputed statement of Sunni creed.
An account of ordinary reasoning may describe natural capacity, learning, evidence and valid inference without thereby demonstrating the existence or operation of that model. Such additional metaphysical claims require their own argument.
The lesson is methodological: accepting the efficacy of reason does not commit one to every philosophical theory in which the term “intellect” appears.