It's a distinction between Revenue Churn and Customer Churn. If customer A cancels their account, it is a loss of 1 account. You can't really have negative customer churn.
Revenue churn would be Customer A cancels their account which was worth $5/month. But if customer B upgrades their existing account by $10/month, you would have negative revenue churn. The negative churn here is negative Revenue churn, ie. upgrades outpace cancelations.
Revenue churn would be Customer A cancels their account which was worth $5/month. But if customer B upgrades their existing account by $10/month, you would have negative revenue churn. The negative churn here is negative Revenue churn, ie. upgrades outpace cancelations.