Bridge Problem

Every year, my parents give me a bridge calendar for Christmas. I'm using and enjoying it more than ever this year. Most of the explanations are reasonable and make sense. A few weeks ago, however, I came across an explanation that I just don't understand.

Here's the problem description:

Looks like a heart and a diamond loser to me.

Maybe I don't understand what "second hand low" means, but it sure looks like if East leads his J when he gets in, he's still got his 10 waiting to take your fourth diamond.

Any ideas? Is it just a mistake by Mr. Alder?

I know at least one Life Master reads my blog...