Yes. Humes based his conclusion on Dr. Gregory's initial description of the fragments, which Gregory wrote on 11/22 shortly after the surgery when everything was still fresh in his mind (CE 392). Gregory wrote that description before he knew what he was supposed to say, before it became apparent that CE 399 could not have been the bullet that left fragments in Connally's wrist. Year later, Gregory changed his story and claimed that the fragments were only tiny flakes, but this is not how he originally described them.
Moreover, Nurse Bell repeatedly explained that the fragments were not flakes but were were identifiable pieces of metal anywhere from 3 to 4 millimeters in length by 2 millimeters wide. This squares with the recollection of one of Connally's other surgeons, Dr. Robert Shaw. Interviewed for the award-winning 1988 documentary Reasonable Doubt: The Single-Bullet Theory, Shaw said, "I am sure that the bullet that inflicted these wounds on Governor Connally was fragmented much more than this bullet [CE 399] shows."
BTW, Humes wasn't the only autopsy doctor who recognized that Gregory's operative record of the wrist fragments ruled out CE 399 as the source of those fragments. Asked if CE 399 could have been the bullet that struck Connally's wrist, Dr. Pierre Finck, answered, "No, for the reason that there are too many fragments described in that wrist," and he based this conclusion in large part on Gregory's operative record.
And how do WC apologists explain this evidence? Let me paraphrase: "Oh, umm, Dr. Gregory's initial description of the fragments in the operative record was 'mistaken,' even though he wrote it shortly after the surgery, and Nurse Bell was 'mistaken' too, even though she consistently said the fragments were not flakes, and even though she saw got a long and close look at the fragments! Mistaken. Mistaken. Mistaken."