Depends on where you saw it. If it was at a model railway show or similar then it's probably correct. A 4mm scale narrow boat model. A lot of modellers incorporate a canal in their layouts.
But surely it should be
OO▸ scale not OO
gauge? How on early does four foot eight and an alf, or 16.5mm, refer to a narrow boat. Gauge if anything would be 7 foot, or 28mm, for a narrow boat?