Yes...and thumb UP (perpendicular to the strings). In the '70s, it was explained that you hold your hand as though you were "thumbing for a ride". Now strike the "E" string.
...a lot of the craziness started with Stanley Clarke & "Lopsy Lu" (Open-Hammer Plucks). Then others ran off with that technique (like Wooten).
Two guys with slap/pop technique
& teacher cred-
Dave Larue
Alex Sklarevski
...they have a way of breaking it down & making it very approachable.
For example, Flea's thing on "Aeroplane" is only a constant thumb-pop motion with the RH. The combination of muted/played notes done with the LH is where it's at.
Way back, Larue's column in
Bass Player had a great article or two on Left-Hand Slap & how to integrate that into the thumps & pops employed by the RH.