Fairly simple question here (I assume).
Could frequent Ne/Si use easily be confused with Se-dom? If so, why?
Ni-doms have inferior Se. When Ni-doms do activities that require high use of Se, such as driving, they can be very good at it, so long as they are doing it on autopilot, and letting the subconscious control the reins. Similar thing for Ni-aux and Se-tert, except that the tertiary function tends to be the function one retreats into when stressed. So an ENxJ might go for a drive when he wants to cool off, and if he's really stressed out, he might start spending a lot of time in Se-related activities.
Works the other way too. Se-doms who are on autopilot, probably become brilliant schemers without realising.
How can we tell them apart?
Look at how and when he is doing Se-related activities.
Is he regularly suggesting to play sports? (Se-dom)
Is he suggesting to play sports, to help resolve a problem, such as when no-one can agree what to do? (Se-aux)
Is he choosing to play sports a lot when he is stressed? (Se-tert)
Is he great at sports when he is not paying any attention to what he is doing, and on autopilot, much more than normally? (Se-inferior)
Not tested this stuff yet. But it makes sense to me, from the theory.