I need to present a scenario where looking at an average (mean) difference between two groups on something might be misleading. and explain why looking at this mean difference might be misleading. I came up with this scenario. Is it correct?

If we compare two groups of depressed patients, group A=50 patients receiving inpatient treatment, and group B=100 patients receiving outpatient treatment, with 10 of these patients attending a depression support group, the mean between the two groups can be misleading due to the difference in treatments and also due to the 10 outliers in group B.

Do I need to include more information to explain why it is misleading?