The documentation is correct here; none of the examples you show demonstrates implicit concatenation of string-valued expressions.
The tutorial documentation is referring to two strings placed
directly next to each other with no other syntax (other than
whitespace) in between.

For example, taking just the first line you give (after the definitions):

    print(s1, s2, "\n", s3, "\n")

Nowhere in this line are two string-value expressions placed right next
to each other; they're occurring in an argument list to a function,
separated by commas. The other lines are similar.