Bit of an essay (oh and look prime essay writing time it is too) 
Well IF they said that they're talking nonsense cos they can't do that, plus a rant is unprofessional. Likely to be a misunderstanding in terms of what was said as pps have said 'I feel like/am tempted to... 'Will be writing to your home ADDRESS'.
When I was at uni if your attendance was shit, you lost your place.
1st time (nursing) everything was compulsory and unless you had a GREAT reason (practically dying yourself or death or serious illness of immediate family) you'd damn well better be there!
2nd time was after fees and loans had come in and you had to sign in. If attendance fell below I think it was 90% without a really good reason SLC could be informed so you'd risk losing your funding and of course your place. One arrogant sod got his arse handed to him cos he thought as his marks were always 70%+ he didn't have to go, but that was in 1st year and he was warned that subsequent work got harder PLUS lack of attendance was not acceptable and had consequences.
I also noticed lecturers and professors were more likely to have time for committed students than the ones that are hardly there and put in minimal effort.
As a student I also really got annoyed being in group assignments with lazy arses!
Actually you seem to have a somewhat romanticised 'my child would never do that' view of your child. The fact she is so concerned about this that she called to give you a 'heads up' suggests to me that there's a possibility her attendance ISN'T great, also that she's a bit immature and lacks resilience!
My dds 16 if she were at uni now and they tried this her response would've been 'aye right! For starters you'd be in breach of dpa, for another not much point ranting at us when we're the ones that ARE here' 
And yes the idea of my uni's using my parents as a threat when I was 21 the first time and in my THIRTIES the 2nd is ridiculous! 
"I studied with a 17 year old, so they were a child." Here in Scotland people can attend uni from the age of 16 as a norm. When I went to 6th form college in England in the 80's my college did not communicate with my parents as it was post compulsory education so legally for that purpose I was an adult.
I agree, some lecturers are always more engaging than others but lack of preparation or poor teaching is no longer tolerated (in addition to having been a student I have friends and relatives that work in tertiary education, one is a dept head.) They can't afford to tolerate that now.
Frostyfingers while I get you were worried as your son is I'm assuming an adult with capacity legally, it's not the universities place to parent him or you. There are students estranged from their parents who may even be at risk from their parents so universities risk being culpable in disclosing the location of someone at risk. In addition as you phoned they have NO certainty that you are who you claim to be (one of the mature students on my course had a violent ex who'd called claiming to be her father needing to tell her that her mother had become seriously ill. Utter bullshit he was just trying to track her down! Can you imagine the shit the uni would have got for disclosing she was at their uni?!) If an ADULT student doesn't wish their parents to be given any info that is their right. As he's now left the uni why do you expect ongoing support for him from them? They have no responsibility to him whatsoever!
"He's an English Lit prof and had the temerity to ask a student a question about the set reading she was supposed to have done (but it transpired that she hadn't)." Haha I have to say I found it amusing that students were caught out that
the lecturers knew about gradesaver etc too and would ask questions that only those who'd actually read the text could answer. 
BlueDa - be careful, sounds like you're in a tough situation but the uni has to serve its own needs. Have you spoken to student support services? Shelter? I was a Lp 2nd time it's bloody hard. Are you getting everything you're entitled to? I'd rather not derail but if you want more info or to chat pm me. Aside from everything else 3rd year is very hard and you don't have to take all the burden yourself. Good luck.