Smothered can describe two very different situations. Literally, to smother someone means to cover their nose and mouth so they can't breathe — so 'he was smothered' describes someone being suffocated that way. Much more common in daily life, 'smothered in/with' something means completely covered by a thick layer of it, especially food: 'fries smothered in cheese' means piled high with cheese. It can also describe a feeling — to feel smothered by someone means feeling like they're giving you so much attention or control that you can't be yourself, especially in a close relationship.