This is just them being explicit that the capital gains is calculated including the sale of fund shares:
"In calculating the capital gains taxes (or the benefit resulting from tax losses) on a redemption of fund shares, the federal tax law netting rules should first be applied to losses and gains from the sale of fund shares. A fund should only assume that a shareholder has sufficient gains of the same character from other investments to offset any capital losses from the redemption after the fund has netted all gains and losses from the sale of fund shares."
https://www.sec.gov/divisions/invest.../mutualq-a.htm
As you indicate, it shouldn't matter within a tax sheltered account.
Also, I suggest you immediately go to
https://www.bogleheads.org and spend some time in the wiki:
https://www.bogleheads.org/wiki/Getting_started
(normally I stay off OT threads, but this is a quasi-PSA
