the way the sound doesnt continue after a certain point leads me to believe that that's just the kick sample itself
My exact thought.
...but the sample had to be made somehow. I think it is a reverb, but skillfully mixed in. No pre-delay, lot of modulation. They probably had input lowpass and highpass filters (and/or dampning) set so the tail is not grainy and also it doesn't clash with the bass. Probably mixed the reverb's output independetly for further EQing.
