A one day of missing school food does not necessitate a cause for concern

However; if there is a continual missing of lunch-time and or school dinners' for more then a valid period of time :

A three to four week pattern, then a forwarding record can be kept and other concerning authorities' noted; this is for extreme cases' whereby there is a dramatic loss in weight and or other.

However; if after a school interview, of parent teacher collaborations', there is a valid reason for such child characteristics' of abnormal behaviour, for instance, a death in the family, a holiday of parent vacation, a change in routine, a change of parent(step), or other valid and sustained reasons' why they would be such a patten of unusual behaviour, then the school can note it as a watch until a normal sustaining routine is established again.
These a natural child like characteristics' of silent protest, not necessarily abuse of parenting, though in some cases' it can be.

If the child seems to be deteriorating in the line of weight-health and or other, then a cause for concern and notification be handed to the appropriate authorities' of concern until further notice.