You're right. From wikipedia:
South Asia consists of the following territories:
Bangladesh
Bhutan
India
Maldives
Nepal
Pakistan
Sri Lanka
Tibet
The United Nations subregion of Southern Asia (see Subregions of Asia) includes the above plus:
Afghanistan
Iran
Southeast Asia frequently refers to the area consist of the following, although in general and certain specific usage, the area it refers to can be broader (e.g. including the southern coastal China as well as Bangladesh, South India, Sri Lanka, and Maldives) or narrower.
Brunei
Myanmar (formerly Burma)
Cambodia
East Timor
Indonesia
Lao PDR (Laos)
Malaysia
Philippines
Singapore
Thailand (formerly Siam)
Vietnam
All of the above are members of the Association of South East Asian Nations, except Timor Leste, which is a candidate.
I got that answer a couple of days ago to my similar question, but I STILL think it is dishonest to call Arab Muslims "Asians". It makes it sound like we're (unfairly) profiling Japanese or something. . .(grumble, grumble).