Chromosomal order of supplementary alignment in BAM file "SA" tag
There is nothing in the SAMtags specification that dictates the order of the entries in an SA tag.  It may be entirely dependent on the aligner that you used.

Looking at my own data that was aligned with bwa, I cannot see a definite pattern.  Longer matches tend to be first, but not always.

Your aligner documentation may have more information on how it uses SA tags.