I don't work on self driving cars or even vision, but I have heard when you are on a highway you start with filtering out small stationary reflections, since they are almost certainly not cars. (Which is maybe why the tesla didn't see the big red firetruck - it was not visible). It's not a big leap to imagine that Uber's LIDAR ignored the bike because it was not recognized as a person, was moving perpendicularly at a low speed, so got pre-filtered as a puddle. We can only guess and Uber will report whatever they want.