More like nibbling — actually, it looked more like they finished the whole thing.
Literal
Snacking [quotative-と] say [question-か], completely-ate-was [like-ように] seemed [though-が].
と言うか ('or rather / I mean') is a discourse connective for self-correcting or reframing what one just said — extremely common in spoken Japanese. つまみ食い 'nibbling' refers to snacking on small bits; 完食 'eating everything' is its opposite. ~ように見える is the standard 'looks like / seems as though' construction. The final が is the trailing contrastive conjunction ('though...'), leaving the thought open — a characteristic soft close.