I see the issue was that once Vettel had the car back under control he then squeezed Ham. A racer's instinct but certainly not within the rules. From motorsport.com, autosport carry the story too:

The stewards examined slow motion footage of Vettel's actions from the moment that he had regained control and started steering his car – and it was felt that it showed that the German could have chosen a different path than the one he took.

The footage clearly captures Vettel correcting an oversteer moment as he rejoins the track – which is shown by a sharp steering wheel movement to the right by the German.

Shortly after that, however, Vettel has dispatched the oversteer and begins steering to the left to follow the direction of the circuit - suggesting he is now under control.

But a split moment later, rather than keeping to the left, Vettel is shown to release the steering wheel which allows his car to drift to the right – cutting off the route that Hamilton would have taken had he had clear space.

The movement to straighten the wheel, which put Vettel into the path of Hamilton, is believed to be key to the unanimous decision by the stewards to punish Vettel.

A further reason the stewards established was through the use of an extra CCTV camera view of the incident, which was not broadcast on the international feed, showing Vettel's head looking in the mirrors at where Hamilton was during these moments when he was releasing the wheel to the right.

Onboard footage of the Vettel incident also shows his head looking towards the mirrors in the moment when he is drifting out, suggesting he knew where Hamilton was.

Had Vettel kept his car tight to the left once he had regained control, then there was likely enough room to have allowed Hamilton through on the right, in which case the matter would almost certainly not have been investigated.

The fact that telemetry data showed Hamilton had to brake to avoid the collision with Vettel showed how the Mercedes driver was caught out by his rival's actions.

Precedent for the Vettel decision to punish him for both rejoining the track in an unsafe manner and forcing a rival off the track was made last year in Japan when Max Verstappen was punished with a five-second penalty for a collision with Kimi Raikkonen at the chicane.

Verstappen had run wide at the chicane on the first lap of the race and rejoined in an aggressive manner, pushing Raikkonen wide on the exit.

At the time, the late F1 race director Charlie Whiting said: "You are required to rejoin safely and Kimi was there and pushing him off the track. So I think that was a fairly straightforward one for the stewards."

For goodness sake, using Chandhok's analysis as 'evidence'!