As per the latest CBSA operating manual, landing officers can only deny entry if, and I quote, "they have reasonable grounds to suspect that the person is inadmissible on grounds of security or for violating human and international rights" (ENF 4, page 17). Under section 11.3 of the same manual it is stated that IF the person claiming PR status lacks documentation, the officer must cross check with the FOSS system and that once status is established, the person "should be allowed to enter Canada without delay". There's NOTHING about the Canadian partner needing to be present upon landing.
I'm not saying the officer denied entry to your husband just to be an ass, maybe he was 'just' incompetent or misunderstood something. You should definitely pursue this.