However that only pushes the question back one level: why did he admire Osama bin Laden? I suspect that that's what his father meant by his statement.
You may be right, but it seems just about everyone else, except his father (taqqyia) knew of his admiration for Osama.
"His uncle, Tahir Pervaiz, told the Pakistani daily Dawn: “Osama bin Laden was Shehzad’s ideal and he used to discuss the man with his cousins and friends in the village.”
http://www.timesonline.co.uk/article/0,,22989-1704235,00.html