Musk is technically very clever (have you seen SpaceX rockets landing in tandem?)s o it's likely he has something that comes close to what he's saying. If so, I expect the real problem with this system will be safety. Sure you might be able to squirt a high density gas or liquid at high enough speed to move this car but then what is that high speed fluid going to hit? Probably it would tear up roads, cut down trees,…
This was done in the 90s, there's nothing special about landing rockets upright. https://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X
Also, being technically clever includes being able to navigate the problems that you brought up, such as the need to meet government standards, meet safety requirements and actually be useful.