So the simplest distinction is sort of text-bookish but all I could think of today :
Kaigi ga owatta = Meeting is over/has ended (simply finished)
Kaigi ga sunda = Meeting is over/been brought to an end/finished with/finished off/has ended (but took some effort to get there).
Sumu often has connotations of finishing off something troublesome or emotionally unpleasant. But it can be interchangeable with owaru there and on other occasions as well.
Go with whatever the book says. I wouldn't sweat it too much at this point.