Altium Library *.LIB to *.IntLib
It sounds like you downloaded a SPICE model, not an Altium "Library" per se.

Altium has:


SchLib -- Schematic Library (A collection of schematic symbols)
PcbLib -- PCB Library (A collection of footprints)
CmpLib -- Component Library (used with Altium Vault, a collection of Components)
IntLib -- Integrated Library, a compiled together combination of SchLib + PcbLib
DbLib/SVNDbLib -- Libraries that hold collections of components, usually described with a database (MS Access or similar)


FWIW, even if you just have a singular symbol or footprint, it'll show up as a SchLib/PcbLib.

As you found out, you can attach models to components in Altium such as SPICE or IBIS -- if I recall correctly, that linking can be done either at the SchLib level, or I think the Vault may support linking of models at the CmpLib level as well.