Julia Child beef bourguignon question
I agree the original instructions are unclear, but "return the beef and bacon to [the casserole]" implies that the "beef and bacon" includes the other ingredients cooked in the casserole - the onion and carrot. Sometimes recipes refer to mixtures by their predominant ingredients, and this recipe seems to do this, albeit a little vaguely.

Looking at similar techniques, while onion could be used to impart flavor and then removed, there isn't really a good reason to add carrot if it will be removed later. Unless browned, carrots don't tend to add much flavor after removed.

The instructions also say, "Pour the contents of the casserole into a sieve set over a saucepan." This would include the sliced carrots and onions, and sliced vegetables should be large enough so as to not pass through a sieve, so it shouldn't be much of a hassle to separate them from the sauce.

Here is where I found the recipe online.