See, that's a problem. That stands out more than any of the good things that he might say. People talk and things come out and shit happens, but deliberately going behind someone's back for back-channel references is just plain unprofessional, if not unethical. This is the kind of behavior that has the rest of the country (in which ethical standards aren't seen as old-fart ideals to be "disrupted" but are actually considered important) thinking that we, in tech, are a bunch of immature psychopaths.
The back-channel reference check is an unprofessional show of power-- like waving a gun around at work-- because it takes social access to get any information out of it (people don't just offer candid opinions up to complete strangers). What's communicated by the back-channel reference check is "your colleagues are more loyal to me than to you". There's a fucking reason why people outside of tech consider it unprofessional and borderline unethical.
It's not unprofessional or unethical.
> The back-channel reference check is an unprofessional show of power-- like waving a gun around at work-- because it takes social access to get any information out of it
For it to be a show of power, such an action would have to involve "showing" something. It's actually an attempt to avoid hiring bad employees -- that's the benefit people get.
> (people don't just offer candid opinions up to complete strangers).
This merely raises the threshold of badness before they might offer negative information. If their coworker was bad enough, they would. And do.
> What's communicated by the back-channel reference check is "your colleagues are more loyal to me than to you".
The miscommunication is on your end.
(Also, your former colleagues don't owe you or some potential employer "loyalty.")
Also, in the USA, there are rules limiting what you can say about a former employee. By giving a negative back-channel reference, you and your employer might be susceptible to a lawsuit. However, actually suing a former employer for something like that is probably a bad idea, because (1) it'd be hard to prove it (2) it would make you even less employable when other people find out about the lawsuit.
If I ever am in a position to do hiring, I probably wouldn't do it, because I'd trust my judgement more than someone else's.