The one ISTP you know doesn't have to fit every ISTP stereotype to be an ISTP. Maybe he places unusually low emphasis on Se. Some ISTPs focus on Ti+Ni and have trouble relating their ideas directly to anything real in the external world...working on Se is usually the cure for this.
ISTPs tend to be less interested in understanding systems that can't be applied to some kind of "real" process that can be envisioned and understood directly. Like say...quantum physics. A lot of that stuff is pretty abstract and hard to relate to anything real. Much more the domain of NTPs (though I'm sure there do exist STPs who are interested in it.)
There's nothing social about it--consciously applied social cues are more related to Fe. This is about the dynamics of physical mannerisms that people unconsciously exhibit and that can be mapped out and exploited to build a more complete model of how that person operates.
As types with inferior Fe, they're not usually too interested in social niceties because that doesn't relate to mapping out any systems they find interesting.