There are 9 actions described in the PHB. When the spell is cast it describes another action in addition to these. This is just like Dragon's Breath or Witchbolt. The action is what is described in the spell.You're assuming two separate categories of action. That's begging the question. The spell doesn't specify whether the action is Attack or Non-attack, just that the caster uses their action. \
The wording would be different if you attacked with it using the attack action. Green Flame Blade and Shadow Blade are examples that do that.