Where they have reffered to the SEA Games as an 'event' on the whole, 'IS' is used, and where they have referred to the 'components of the event induvidually' (the particular games in this case), 'ARE' is used.
As an example:
The Conference is worth participating in.
The aspects/modules of the Conference are worth participating in.
(I'm not a teacher, a teacher will guide you better!)