In retrospect, President Eisenhower was not correct when he expounded his domino theory. The dire consequences of the loss of Vietnam that he warned of did not come to pass.
When Vietnam fell to communism, it did not set up a chain of falling dominoes. It is true, of course, that some nearby countries did become communist. For example, Laos and Cambodia became communist countries. But that did not lead to a more widespread expansion of communism. Thailand did not become communist. Indonesia and Malaysia did not become communist. The Philippines and Japan and Australia most certainly did not become communist even though Eisenhower at least implied that that might happen.
Of course, Eisenhower could not have known this and so we cannot blame him too harshly. He had to think about what might happen instead of only thinking about things that were certain to happen. So, while he was wrong, his theory was surely at least plausible when he put it forward.