"Our SLAM algorithm is notable for being able to run in real time with not just one, but three Ouster OS-1 devices at the same time, on a typical desktop computer CPU."
It's using ICP to register sucessive lidar scans. All three lidars are calibrated so the relative positions are known and the data from all three can be combined.
https://en.m.wikipedia.org/wiki/Iterative_closest_point
This alone isn't SLAM but can be used for odometry as part of a SLAM system.