How did the pheasant look? Thin, injuries, discharges, flown into a wall..? Where was it? - tucked away under a hedge (because it was feeling ill) or in middle of lawn (dropped by fox?) Pile of feathers?
Basically no, I wouldn't be worried, but keep a eye for any symptoms in your birds and any more birdie bodies. (Although it's the sort of thing that if you start looking, you'll start seeing dead birds everywhere!)