You shouldn't trust people who claim to know 4 digits of accuracy for a forcast like this.

You shouldn't trust a human person who makes that claim. But if we are using 'person' in a way that includes the steel-Vulcan from the quote then yes, you should.

The uncertainity involved in the calculation has to be greater.

It is all uncertainty. There is no particular reason to doubt the steel-Vulcan's ability to calibrate 'meta' uncertainties too.

In the face of all the other evidence about the relative capabilities of the species in question that the character in question is implied to have it would be an error to overvalue the heuristic "don't trust people who fail to signal humility via truncating calculations". The latter is, after all, merely a convention. Given the downsides of that convention (it inevitably makes predictions worse) it is relatively unlikely that the Vulcans would have the same traditions regarding significant figure expression.