Q: "A man in a blue-plaid shirt and white hat, backdropped by a stone wall performs an unknown task while standing atop a platform." Does this mean that "A man stands on top of something."?
A: yes

Q: "A man in a black shirt and cap playing piano." Does this mean that "A black man, wearing a black shirt and cap playing the piano."?
A: it is not possible to tell

Q: "Three men dressed as roman soldiers resting on some steps." Does this mean that "The men are sitting down."?
A: yes

Q: "a man in a black shirt is rollerblading past a bench in the city." Does this mean that "A man enjoys rollerblading"?
A:
it is not possible to tell