I was going to suggest that you make sure to have use strict; in your code, but then I realized that stricture doesn't help in this case. What the OP code was doing is equivalent to:

sprintf( {"string1", $string2} )
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and that is not a syntax error or any kind of violation of strictures or warnings, despite the fact that it is something you would never really want to do (i.e. passing a hash reference as the first and only parameter to sprintf).