Description
Seed features are identified by a value of 1 in the seed field. One seed feature is needed to grow each group. The tool found fewer seed features than groups (Number of Groups parameter). Consequently, the tool will select the additional seed features needed to make up the deficit.
Solution
If you don't want to see this warning, you can modify the seed field you provided so the number of seed features (values of 1) matches the Number of Groups you specify.