its like saying there are two meanings of the word "sweet" one meaning means as in tasty 사탕 e.g. 'this candy is sweet' the other meaning is loving 달콤 e.g. 'you are a sweet guy'
for this 맞아
맞아 (right) e.g. 그것은 맞아요 (thats right)
맞아 (fit) e.g. 이 셔츠는 맞아요 this shirt fits
Hope that explains it all...
Many languages (especially archaic languages or aspects of languages) rely on the same words to mean right/true, just, and fitting, so this doesn't surprise me. Even English has relics of this. For example, the word "right" in English means both correct factually, and morally proper; yet the most symmetric (fitting) angle (a 90 degree angle) is called "right" (a "right angle"). Additionally, "justified text" is text that is made to fit the width of the page. And the word "judge" (and "judgement") relate to truth of falsehood as well as moral goodness, just like the word "right."
Since similar relations between these concepts can be found in seemingly unrelated languages, it does not surprise me that 맞다, usually translated "to be right," could also mean "to be fitting" or to "fit."