Jesus strictly warned them not to tell this to anyone.
Read Luke 9:21 Using Other Translations
And he straitly charged them, and commanded them to tell no man that thing;
And he strictly charged and commanded them to tell this to no one,
Jesus warned his disciples not to tell anyone who he was.
Scripture quoted by permission. Quotations designated (NIV) are from THE HOLY BIBLE: NEW INTERNATIONAL VERSION®. NIV®. Copyright © 1973, 1978, 1984, 2011 by Biblica. All rights reserved worldwide.
(New International Version Bible Online)