As per spec:

In the plaintext footer mode, the optional ColumnMetaData meta_data is set in the ColumnChunk structure for all columns, but is stripped of the statistics for the sensitive (encrypted) columns. These statistics are available for new readers with the column key - they decrypt the encrypted_column_metadata field, described in the section 5.3, and parse it to get statistics and all other column metadata values. The legacy readers are not aware of the encrypted metadata field; they parse the regular (plaintext) field as usual. While they can’t read the data of encrypted columns, they read their metadata to extract the offset and size of encrypted column data, required for column chunk vectorization.

Current writer writes stats into plaintext part of footers too. We would want to write stats into encrypted part of footer only as per the spec.