Not to mention land improvements (grading hundreds of miles of land is not cheap), connecting this to the electric grid (because we get storms that last more than a few days, so solar+batteries isn't going to cut it, support structures like a yard for doing car maintenance, administrative buildings, all the R&D necessary to test this concept and build the device at the end that turns around cars, putting in pillars that can actually support a big rig full of fuel slamming into them (especially on I-5).
Oh and there's the fact that he's saved a ton of costs by not actually going to San Francisco or downtown LA, but rather Oakland and the edge of LA. He certainly doesn't stop at any of the 14 stops that CA HSR does or replace/upgrade two full metropolitan transit lines (Caltrain/Metrolink).
Really these two things aren't remotely comparable. It seems to me this experimental proposal providing a fraction of what CA HSR offers was put forward purely to derail CA HSR.