As Trump recited the Oath of Office, he never lifted his left hand to place it upon the Bibles. Was it a mistake?

Donald Trump raised his right hand while placing his left hand on the Bible Monday afternoon. He then took the oath of office and was sworn in as the 47th President of the United States.

Some presidents did not use a Bible to take the oath of office, including Theodore Roosevelt, who did not use anything when he was sworn into office in 1901, and John Quincy Adams, who chose a legal book for his 1825 swearing-in, to signify his responsibility to uphold the U.S. constitutional law.