You are correct, at least according to the B::Deparse documentation. Interpolation is just syntactic sugar for concatenation. You can see it for yourself:

$ perl -MO=Deparse,-p,-q -e '$foo = "BAR"; $bar = "a${foo}c"; $baz="a"
+.$foo."c"'                        
($foo = 'BAR');
($bar = (('a' . $foo) . 'c'));
($baz = (('a' . $foo) . 'c'));
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Update: Added concatenation to the example for comparison. Also, the output using B::Terse to dump the opcode tree may be more convincing.