No! That’s not true. The clerk during the ceremony called all their names to make sure that they aren’t there.That's true, but I am certain that IRCC had previous knowledge of their absence (I don't think these empty seats were for people who decided not to show up), and could have filled these seats with others who have been waiting for the oath for months.
The invitation clearly says that if you cannot attend ceremony let IRCC know in advance. That means these people weren’t serious about it. There was more than 10 people absent.