A quick answer is that all cell groups are small groups but not all small groups are cell groups.
Small groups can meet specific needs of the group members.
Small groups have a history of benefiting the body of Christ especially in time of revival. Cell groups are a specific type of small group and a type of small group that has a specific model of ministry. Most small groups are one of the programs offered by a church congregation. Most basic unit Cell groups are not a program of the congregation. They are the most basic unit of the congregation.