He apologized. That’s amazing in the corporate world. This suggests to me that they could merely be disorganized rather than disrespectful. (Indeed hiring you may be a desperate attempt to lower the workload on key people.)
So go to the second interview, but don’t go in blind. Pay very careful attention to organizational issues. Pay very careful attention to employee demeanour and treatment. Be ready to ask some pointed questions. Remember that the job interview is two directional: you are interviewing them every bit as much as them interviewing you.