Tesla seems to disagree with you as well, they call it a "multi-mode suction system" [1] suggesting that the evacuation under the car is what does the job. And that's far more likely than that the ejection of that little bit of air at the top is what keeps the vehicle planted upside down. But with vacuum that is almost a trivial accomplishment.
[1] https://x.com/Tesla/status/2110907039493038577 ; third slide; caption under the photo.
"Multi-mode fan & ground sealing system pulls air from beneath the vehicle, generating enough suction to hold it upside down while stationary"
I'll just note that again, my hypothesis and the actual way it works are very similar to each other, and both are very dissimilar to the suction cap analogy. Suction cap works by utilizing atmospheric pressure, this utilizes moving a large amount of air in the direction opposite to the road. The only difference is that it's taking the air from below instead of pushing from above. I imagine that is the case to utilize the same outlets that are used for lifting the car.