The article you link mention they found a damaged drone on the ground. That doesn't sound like evidence of "no drones" to me.
That's what the article is saying though. That the entire origin story of "drones over Gatwick airport" is that someone found a damaged drone. That doesn't mean that the damaged drone was ever "over the airport", it just means someone found a damaged drone. No mention of how close to the airport, how long the drone had been there, etc. It could have been in a park nearby and someone crashed it into a tree weeks ago and it fell to the ground more recently.