The model shows Locations, Equipment, and Points. Nothing can appear under a Point. You’ve not even tagged your Group with a Point tag, let alone an Equipment or Location tag. You’ve only applied the Property tag “temperature” which is pretty much meaningless to the semantic model. I’m surprised it shows up at all.
To tag it properly, you need to add a Point tag to indicate what sort of temperature this Item represents. “Measurement” probably makes the most sense since it’s the average of other measurements. But even once you do that, none of the members of the Group will show up under this Group because it’s not an Equipment nor is it a Location.
You might want to review/rereview Semantic Model | openHAB and remember, not every Item belongs in the semantic model in the first place. The model is there to represent the physical layout of your home automation controls only.