I believe you're looking at this issue through the eyes of a technical person who understands those distinctions. There's a huge group of sites and apps catering to entirely non-technical folks to whom that distinction would only bring confusion.
For a software bug tracking app, I can see why you'd want this. For a store that sells something like cloth diapers, I think it would be confusing (at absolute best) and certainly not any kind of improvement for either Heroku's customer or their customer's customer.
That's correct. I certainly am not pretending to speak for all consumers in all situations, which is why I stated it can matter.
My primary point was that since it can matter, the information should be presented. An underlying assumption being that it can't hurt, but could help.
However, you brought up a point I hadn't fully considered : namely that this information could be directly confusing to some users and by extension undermine their faith in their service provider.
That said, I think the sample error message in the OP is sufficiently clear for the broad spectrum of users. Therefore, I believe presenting users with that message, or something similar, would do more good than harm.
But how do you know what kind of users Heroku's customers' customers are? How do you know that none of them are technical users? How do you know that none of Heroku's customers are running a software bug tracking app?
I don't know; but your comment suggests you're missing my point entirely. It's not about what each individual customer does; it's that implementing such a feature across the board might work well for Heroku customers whose own customers are technical; but, would fall down big time for those whose customers are non-technical.
For a software bug tracking app, I can see why you'd want this. For a store that sells something like cloth diapers, I think it would be confusing (at absolute best) and certainly not any kind of improvement for either Heroku's customer or their customer's customer.