If it is the two soft rubber hoses approx 40mm diameter that are securely fixed with jubilee clips and are clearly not radiator water hoses then it sounds like the turbo hoses.
If one comes off with engine running, performance will drop right off and with bonnet up you would feel air blowing out of one.
Re oil spray? If it is inside the hose going towards the engine inlet manifold , it can indicate worn turbo bearings causing the oil that lubricates the turbo under pressure to leak into the inlet side. However if only a little oil and on an older high mileage engine I would just keep an eye on it.
If the oil was on the outside, could it be diesel from the fuel pipes you were repairing?
Unlikely to be able to fit the hoses wrong way around due to different lengths etc. and usually on inspection , it would look wrong.