SQL-Server/Access - Order BY 1,2?

I came across a query today,

SELECT col1,'yes' as col2  FROM myTable  
   WHERE col2=TRUE  
UNION  
SELECT col1,'no' as col2 FROM mytable  
   WHERE col2=FALSE  
ORDER BY 1,2  

I thought it would order by first column and then second but since a UNION is involved I am a bit unsure can someone explain the exact meaning of this query