Document expected behaviour

parquet/src/arrow/async_reader/mod.rs

@@ -572,7 +572,15 @@ impl<T> std::fmt::Debug for ParquetRecordBatchStream<T> {
 }
 
 impl<T> ParquetRecordBatchStream<T> {
-    /// Returns the [`SchemaRef`] for this parquet file
+    /// Returns the [`SchemaRef`] for this parquet file.
+    ///
+    /// Note that unlike its synchronous counterpart [`ParquetRecordBatchReader`], the [`SchemaRef`]
+    /// returned here will contain the original metadata, whereas [`ParquetRecordBatchReader`]
+    /// strips this metadata.
+    ///
+    /// As such, this schema is the same as [`ParquetRecordBatchStreamBuilder::schema`] which also
+    /// contains the metadata, but differs from the [`RecordBatch`]es produced which have the metadata
+    /// in their [`RecordBatch::schema`] stripped.
     pub fn schema(&self) -> &SchemaRef {
         &self.schema
     }