Why does line 16 of index.js produce a Flow error?

.flowconfig

[ignore]

[include]

[libs]

[options]

index.js

/* @flow */
type EncodableType = string | number | boolean;
type EncodableData = { [key: string]: EncodableType | EncodableType[] };

function encode(data: EncodableData): string {
  return "the encoded data";
}

encode({ data: 10 }); // OK
encode({ data: [1,2,3] }); // OK

const data = [1,2,3];
encode({ data }); // OK

const data2: number[] = [1,2,3];
encode({ data2 }); // ERROR

/*

$ flow check

index.js:16
 16: encode({ data2 });
     ^^^^^^^^^^^^^^^^^ function call
 16: encode({ data2 });
              ^^^^^ array type. This type is incompatible with
  3: type EncodableData = { [key: string]: EncodableType | EncodableType[] };
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ union: EncodableType | array type
  Member 1:
    3: type EncodableData = { [key: string]: EncodableType | EncodableType[] };
                                             ^^^^^^^^^^^^^ EncodableType
  Error:
   16: encode({ data2 });
                ^^^^^ array type. This type is incompatible with
    3: type EncodableData = { [key: string]: EncodableType | EncodableType[] };
                                             ^^^^^^^^^^^^^ union: string | number | boolean
    Member 1:
      2: type EncodableType = string | number | boolean;
                              ^^^^^^ string
    Error:
     16: encode({ data2 });
                  ^^^^^ array type. This type is incompatible with
      2: type EncodableType = string | number | boolean;
                              ^^^^^^ string
    Member 2:
      2: type EncodableType = string | number | boolean;
                                       ^^^^^^ number
    Error:
     16: encode({ data2 });
                  ^^^^^ array type. This type is incompatible with
      2: type EncodableType = string | number | boolean;
                                       ^^^^^^ number
    Member 3:
      2: type EncodableType = string | number | boolean;
                                                ^^^^^^^ boolean
    Error:
     16: encode({ data2 });
                  ^^^^^ array type. This type is incompatible with
      2: type EncodableType = string | number | boolean;
                                                ^^^^^^^ boolean
  Member 2:
    3: type EncodableData = { [key: string]: EncodableType | EncodableType[] };
                                                             ^^^^^^^^^^^^^^^ array type
  Error:
    2: type EncodableType = string | number | boolean;
                            ^^^^^^ string. This type is incompatible with
   15: const data2: number[] = [1,2,3];
                    ^^^^^^ number


Found 1 error

*/