Is getting a thrid party to review the results typical?

I can only speak to the engineering field I worked in ( structural and civil ) and the answer is no, it is not typical. The only time a third party was called in for a review was if a client requested it for legal purposes or if something was so out of the ordinary that it had to be reviewed. Nevertheless, calling in a third party was always at the request of clients.

I'm not 100% sure how this works with a BFS so I would assume they are checking these results at the request of a 3rd party (Teck) perhaps? Or something is so out of ordinary that ES is double checking it to protect his back legally. Nevertheless, if that is the case I am assuming that the something so out of ordinary is in a positive way. I doubt that they would hire somebody if the BFS was less than exciting or negative. That is my 2 cents.