Generally, string is a flexible piece of rope or twine which is used
to tie, bind, or hang other objects.
My guess is that the term was simply derived from this, because a sequential array of text just resembles it, including its typical uses. As others said, there are many more meanings to the term in regard to computer science:
In computer programming, a string is traditionally a sequence of
characters, either as a literal constant or as some kind of variable.
The latter may allow its elements to be mutated and/or the length
changed, or it may be fixed (after creation). A string is generally
understood as a data type and is often implemented as a byte (or word)
array that stores a sequence of elements, typically characters, using
some character encoding. A string may also denote more general array
data types and/or other sequential data types and structures; terms
such as byte string, or more general, string of datatype, or
datatype-string, are sometimes used to denote strings in which the
stored data does not (necessarily) represent text.