The yield is only part of the return, one has to consider also the change in price. If interest rates go up prices will go down and the actual return will be lower than the yield.

Over the last 12 months, the price of the VCSH fund is down more than 2%. This offsets the dividends paid with the coupons received and results in flat performance.

Yes. This is a marketing website for Vanguard, so of course they want to list the highest return possible, and dividends definitely do count in performance.