Sure, it's a bit more complicated, but the point here is that Waymo remains an Alphabet subsidiary, external investors are investing under that understanding and with full knowledge of Alphabet’s control of Waymo (which is why the blog entry you link to links to the Alphabet 10-Q reporting the external investments and the resulting “noncontrolling interests” in the subsidiary.

A “spin-off” within a common corporate umbrella is a different thing done for different reasons than a corporate divorce kind of spin-off like IBM is doing.