In fairness, in RL, you would almost certainly either tell the person's answerphone immediately, or at least give them some indication of what you knew, if this key thing you had just found out was so crucial (and you were also slightly pissed/pilled), but this is the land of TV drama, where you always say 'I've found out something really important!' and get killed immediately.
In the spirit of 'I'm confused about some characters in Season 8' sharing, I will admit that until Ruth and Sandy arrived at Cal's house the morning after his death, I didn't know what relation the candle-making man in the wheelchair (James?) was to Cal. I think at one point I thought he was his father, despite not looking anywhere near old enough, or just a housemate, and I think at one point I did consider he might be his boyfriend...? 
But then I've been rewatching old seasons, and Shetland's casting people do make some odd choices sometimes.
In season 7, about the murder of the lawyer Alex Galbraith, there's a subplot about Alex Galbraith having been paying for years the care home fees of a (supposedly) missing girl's elderly father, but the elderly father in question looks in spry good health, and not particularly old at all, compared to the woman who is cast as the same-aged best friend of his daughter, now presumably late 30s or early 40s... (And there was never any resolution to the mystery, which I remember discussing on here, of the 100% male-looking 'nun', in full wimple and habit, who let in Perez when he visited the retreat centre.)