Create different arrays, and then determine if they are string arrays.

Test a character vector.

chr = 'Mary Jones'

chr = 
'Mary Jones'

tf = isstring(chr)

tf = logical
   0

Character vectors are not strings, so isstring returns 0.

Test a string array. Starting in R2017a, you can create strings using double quotes.

str = ["Smith","Chung","Morales"; ...
       "Sanchez","Peterson","Adams"]

str = 2x3 string
    "Smith"      "Chung"       "Morales"
    "Sanchez"    "Peterson"    "Adams"  

tf = isstring(str)

tf = logical
   1

str is a string array, so isstring returns 1.