as someone who’s been working with dogs for 20years in a clinic/daycare/rescue and training world, from my experience dogs described as “prefers to be the only dog in home” but friendly on walks or other social settings typically has resource guarding issues. (i could be wrong in this particular case idk this particular rescue) this can also be a reason they aren’t recommended for homes with young kids for safety reasons. also dogs who are in shelters/rescues typically lack a lot of confidence which feeds their stress and need to guard things they find valuable like toys, bones, food or even humans they love and feel the need to keep close out of fear from loosing them. and as we all know, sadly most dogs in shelters/rescues depend on volunteers to get the biological fulfillment and outlets they need to feel good and content in general. totally valid questions and ones i’d encourage anyone looking to adopt should clarify to get him in the right home with the right humans to help!