The sales volumes resulted from sales in May, and May is when NG prices dropped substantially. Also, it is possible that the costs deducted will be increased in the distribution. The latest 10-Q shows actual costs exceeded deducted costs by about 0.06 per share.
He is probably close to being correct due to the lower NG prices for the past 3 or 4 months. It happens almost every year due lower gas prices April through usually August or Sept. However hotter than normal summers and particularly hurricanes can shorten the so-called shoulder season. I prefer to look at the distributions on an annualized basis, which is easily obtained from the Yahoo page showing historical prices and dividends [ actually distributions] I believe last month the 12 mo. trailing distributions were about $2.60, which gives about a 9% yield on todays closing price.