I wouldn't be as anxious as you seem to be about this.
For sure, if a PhD is knowingly misled as to his future prospects after a particular research programme then that is immoral - and probably also very foolish of the research supervisor from an entirely amoral standpoint: he/she will make a bad name for themselves.
But I wouldn't say that industrial employers are always going to take relevant research experience as their primary criterion in deciding between candidates for research positions. Industry is largely about (or supposed to be) cooperative research and a clear communicative link between candidate and employer's existing researchers in thesis/publications and moreover conversationally at the job interview is what matters most of all, I would say. Cooperability is worth far more than individual brilliance in a team effort.
Sure, it's not nice to see someone sidetracked. But if that person made a decent fist of the project, wrote it up clearly and accessibly and presents themselves positively then they will get a position worthywhere they can show more of their talents. If not, it's time to try another métier.