All it is is that your line: print("$passwords{"Matt"} is my password."); is being interpreted as :

print("$passwords{"Matt"} is my password.");
      ^-- string -^    ^- another string-^
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Effectively making 'Matt' a bareword (i.e. not a function, string etc...)

Always remember to use warnings and strict (and diagnostics for more info on any error messages).

Check out perldata for info on string interpolation... Hope this helps,