I think there's a bit of contact on the left heel, I can see why it was called a foul and once it's a foul it's gotta be a red. But if you watch closely, contact is pretty marginal and I think it could have gone either way. That said I agree, it was a better call than the penalty.
For me embellishment is the horrible part, if that was Zaha or Stirling they would be getting crucified. You can see him feel the little clip on the back of the left leg and after a second delay, arch his back and throw back his head - there's a biased commentary here but the video is decent:
https://twitter.com/user/status/1031651939010916358