FieldGroup automatically displays a LookupField for reference attributes, i.e. links with other entities. Your tenantId is probably a simple data type attribute, so providing options doesn’t help.
If you make tenant attribute a real reference to a Tenant entity in your data model, visual components will reflect this link automatically. Otherwise you have to make a custom field in your FieldGroup, generate a LookupField for it and provide the list of options via setOptionsMap().