The student was increasingly a problem (note the screaming at the advisor mentioned in TFA). The advisor decided that it was no longer worth the effort to maintain the unofficial relationship and broke the promise of supporting the student's future re-enrollment. Dealing with unprofessional students sucks. It's very hard to "fire" grad students for unproductivity or workplace issues, unless they are egregious. In this situation the advisor had a convenient out and took it.