He was slated for options on his first stop but the RBR drivers had "talked over" each other on the radio so the pit crew failed to receive notice Vettel was inbound. Rather than waste more time sorting out the tyre selection, they simply slapped on the primes they had readied for Webber.
I stand corrected. I reviewed the video and I was mistaken. I thought I remembered seeing a red lettered tyre when Vettel was in the pits but it's during Webber's stop that the options are visible. Their stops were so close, I'd thought I was seeing a replay of Vettel's stop when it actually was Webber's.
Which means RBR were gambling they could get 60 laps out of a set of primes. That's beyond audacious, that's positively foolhardy.
James Allen quotes Chris Horner to say the options were put on Vettel's car by mistake. I have not seen that quote reported elsewhere but he normally is pretty reliable.
Will Buxton reported that the RBR pit crew were all at sixes and sevens as soon as Webber had got out of the box. Well-oiled machine that they are, this would also seem to indicate something during the stop had gone awry (apart from Webber's slow stop).
From his own lips, Chris Horner admits Vettel took on the wrong tyres. As race progressed, Guillaume briefed him they would be bringing him in nearer the end of the race to change back to the options, but Seb warned them off, claiming the primes were still fine. Vettel maintains he had enough pace to hold off Alonso to the end, and Horner echoes that. More's the pity, we shall never learn the truth of it. Damned red flag.
This is a fascinating conversation I'm having with myself. Shame no one is listening.