That just means that at current interest rates, the stock's forward P/E exceeds the rate of interest. It's rational to borrow money to buy stock if the earnings spun off by the stock exceed the rate of interest. You're basically arbitraging against the bank: the bank gives you money to buy out people who think the stock is overvalued, you give them a set amount of interest for the money, and if it turns out you're right and the stock's future earnings exceed the price of that money, you pocket the difference at the expense of people who left the market. If you're wrong and earnings are less than the interest rate, it's reflected in net income, the stock drops, and you (and the rest of the shareholders) eat the difference, often in a dramatic fashion.

With low interest rates, high corporate profits, and low growth, I'd expect to see a lot of debt added to balance sheets; it's a way to lever up the capital structure to the benefit of existing shareholders, as long as profits remain high and interest rates remain low. (And corporate bonds/loans are usually fixed interest, so the interest rates are locked in until they need to go back to the debt markets.)