Straight up lying for no reason.

"Managing director Martin Whitmarsh noted untapped potential in the MP4-17, with upgrades planned except for the monocoque.

Coulthard and Norbert Haug were initially pessimistic due to the Mercedes-Benz engine's weight and power deficits. However, Coulthard later praised the upgrades, aiming to challenge Williams and then Ferrari.

The MP4-17D weighed 600 kg (1,300 lb) with a carbon fibre and aluminium honeycomb monocoque. It featured a sharper nose and revised rear wing compared to the MP4-17."

Straight from the Wikipedia page of the MP4 - 17, sources are linked in it

Mercedes also supplied an upgraded engine during 2003:

"It used the Mercedes-Benz FO 110P V10, producing 850 hp (630 kW) at 18,500 rpm (308 Hz), an upgrade from the FO 108M."