ISTP would be a Melancholy-Sanguine (IST-Melancholy; SP-Sanguine. PhlegmaticCholeric borders on Melancholy, so that could still be a fit). It fits common profiles of the MelSan as being very artistic.
In this view, SP is Sanguine in Control. Would figure, because the Sanguine in Control, marked by what those reports call a "dependent/independent" swing, would be connected to Se, which specializes in reacting to whatever is before you in the concrete environment. So the person will aggressively ("pragmatic"-ly) jump on physical opportunities, but then also quickly drop it, when the environment changes.
NT is also "pragmatic", but tends to stick to it longer, because it's all about the "idea" (N), along with the Thinking. This would fit Choleric, that doesn't want to give up on anything.
Again, for most INTP's, this gets toned down in their self-identification (when selecting directly from these profiles) to Melancholy (which shares the same "critical" nature with the Choleric).
Sanguine is unusual for NT's to identify with, though again, does share in the pragmatism.
"Not getting out enough" isn't a good type indicator. While you may think SP's would always get out, for what ever reason, they might not, but the SP part of it simply means that their primary means of taking in information is what's tangible in the environment. You don't have to be outdoors to do this, though it may often lead one outdoors, which of course is a bigger "environment" to explore. Again, anything can change that.
But the type is also part Melancholy, which is often (notoriously) drawn to withdraw and be homebodies. Being diametrically opposite temperaments, there's probably a tug of war as to withdrawing and getting out.