We need more context. You say "Only five items appear in all frames below" but you only tell us about 4 of the items (cell phone, radio, DVD, and TV set).
In general, the word 'items' does not pertain to only 'electrical' things. I am confused by the answer that was given in your son's English book. A hat, a cup, a vase, a tennis racket, and a cap are all items.
Furthermore, a cell phone and a DVD are not technically considered 'electrical'.
Can you provide us with some more context?