Though Tyson prefers not to leave clutter around, he has a tendency to keep hold of old keys.
When he knows a lock has been changed since, Tyson will throw away a key, but until that fact is proven, he will keep that key. Just in case.
No matter how unlikely it is that Tyson will ever return to that place, or that he would have that particular key on his person at the time, Tyson will keep that key as an emergency back up in a little metal tin under his bed.