No, you can eat at any restaurant and don't need to tell the main restaurant that you're eating elsewhere.

luci

Luci, thanks for that.

When on a ship that offers "traditional" dining allthough not required it is a courtesy to let the table companions know if you plan to take the next meal elswhere.

This means they don't need to wait for you thinking you may just be late and gives them the oportunity to invite other people to the table for that night.

If the complete table will eat elswhere then telling the waiter is a good idea.

We do not make a special effort to tell if we decide to eat elsewhere that evening and will not visit the dinning room before the dinner.