We’ve asked Tesla for comment. It has previously welcomed the possibility of allowing Supercharger access to non-Tesla vehicles, but only if they can agree on costs. There’s no agreement so far.
As Electrek suggests, this could easily be a bug or some other flaw. Tesla only allows free Supercharger use as a perk for some of its customers, and it likely isn’t happy that someone with a competing car could not only recharge at its stations without permission, but avoid paying for it. Don’t be surprised if Tesla rushes to block freebies in the near future.