Well, I think it should be the other way around, you first mentor someone
and look with them into their packages and then decided about sponsorship.
That's your opinion, and here's mine: I don't think that's important. If a candidate looks promising and there is an intention to both sponsor (confirming by e-mail that the applicant is sponsored when they apply) and an intention to mentor (at least look through the AUR packages and give them helpful hints), I don't think the order matters, as long as everyone is honest with each other and both things happens before the application is sent.
That's not what happened in this case, though, since the application was sent before there were any mentoring.
Through work, I've had the chance to train about ten employees and interns. I've also mentored two peers of mine. All of these people *looked* promising. They all either got through the job application process or struck me as someone I wanted to mentor. Furthermore, all of them professed a great interest in learning about QE, virtualization, software engineering, and whatever other topics were relevant to them. However, there have been a broad spectrum of outcomes. I'm going to be intentionally vague and say that some were brilliantly successful; others struggled but succeeded after *years* of intense efforts; others realized that they weren't actually that interested in the topic at hand, but only after investing much time and effort; and others failed due to incompetence and/or self-sabotage. Do I trust someone to be trustworthy and competent because they "[look] promising and there is an intention [...] to mentor"? Not at all. This is a comment on the sponsorship for this TU application, not a comment on this TU application itself (which has already been rescinded anyway).