In order to index by a string or categorical in the first index of a table, the values have to have been set as the RowNames property.
filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/730924/Test.xlsx';
Data = readtable(filename);
Data.Properties.RowNames = string(Data.country);
You can see from this that every row name must be unique.
The indexing done with the first index of a table is not equivalent to a SELECT operator that would select all matches. Instead, the RowName that is set must be unique, must identify exactly one row in the table.