Both ”s” & ”ts” are /ʃ/ and /tʃ/ respectively, unless immediately preceded or followed by one another, then ”s” is always /s/ and ”ts” is always /tʃ/.

I presumed the second one is a typo. Also, since this is a section on allophony, it looks like the // vs [] use is wrong, unless the 'alternation' is actually based on a weird orthographic convention.