Yes, to me it looks like dreadful insect damage, this sort of damage is not caused by sunlight or from an improper diet.
Examine your leaves very closely, particularly underneath for what I may suspect might be spider mites, but could be another type of insect too.
Either way, the damage definitely looks like the work of a "sap sucking" insect of some description. Identifying what type of insect it is, will determine your next type of action to be taken. Sometimes when plants are stressed, they become attractive to insects and once the insects have a weakened plant to "attack", they will often continue "attacking" the same plant without spreading to other plants living close by that are with full health.
Hope this helps,........ Organoman.