Don't check isinstance

Author: dsaxton

pandas/core/dtypes/cast.py

@@ -278,7 +278,7 @@ def maybe_cast_result(
         if is_extension_array_dtype(dtype) and dtype.kind != "M":
             # The result may be of any type, cast back to original
             # type if it's compatible.
-            if len(result) and isinstance(result[0], dtype.type):
+            if len(result):
                 cls = dtype.construct_array_type()
                 result = maybe_cast_to_extension_array(cls, result, dtype=dtype)