If you look at that college professor's ordeal, there are red flags everywhere:
Woman approaches him and is far too obvious: strongly compliments him when he doesn't take the first hint and tries to direct her away. Then persists when he brushes her off: "Sorry I just don't know anyone" (persistence line to appear vulnerable/available). Approaching men is super scary, hard, and unusual for 99.9% of women and the best they can usually muster is a single lame joke or boring comment, hoping you will take the reins. When they're able to be present and clear about their intentions, it's usually a sign that either a.) they're experienced enough approaching men that "the game has slowed down" for them or b.) they're psychopaths who don't feel nervousness. Both are large red signs
She's a single mother (at least a yellow flag, usually orange), a single mother to more than one child (orange flag), whose ex is a woman (red flag), and who is currently rooming with a transsexual (red flag). In addition, the (transsexual) roommate is "battling depression", and this is something the woman feels this guy needs to know on the first date (orange flag).
Then she invited him to her place, initiated the kissing herself, and initiated the sex. This can be a yellow flag (I've known marriages that came from the woman initiating intimacy, where the woman was really pretty kind/stable overall, just slightly in huntress mode), all the way up to a red flag, depending on context. Given all that's already happened I'd consider it 'red flag' territory.
I guess it depends on your sensitivity, but I will say that if I see one red flag, I lose a lot of interest in a girl. I might still pursue just to be thorough at that point, but I'll be on-guard, and any further flags will generally lead to me abandoning the lead / ignoring efforts by her to set anything further up.
The hard thing here is this guy was in scarcity. He didn't know how to meet women and had no other women in his life. Men in situations like that tend to ignore red flags much more than they should. The offer of sex is too hard to pass up even in the face of several glaring signals.
From what I know of the forum member's case, there's nothing realistically he could've done to avoid the situation. It sounds like she did most/all the initiating and she left apparently satisfied enough. He didn't say he was pushy at any point or she gave any indication she was unhappy. So unless he did something he didn't realize or she was throwing off signs he didn't pick up on, there wasn't an indication she was going to throw him under the bus later. We don't know her motivation either, if she had a boyfriend and got found out and needed to say it was rape to keep the boyfriend ("I just went over because I thought he seemed nice and I was looking for friends <sob>, I never thought he would rape me!"), or if it was something else. So I can't say "He could've prevented it by asking if she had a boyfriend first and not hooking up with her if she did." I'd be a hypocrite there, too, because I never ask women their relationship status; I don't want to know about it and consider it irrelevant unless they themselves bring it up.
Best thing he could've done was stick to meeting women in real life, where flags are a lot more obvious and he'd be meeting prettier girls. Dating apps encourage men to settle for homelier, more broken women, and the odds of that going the wrong way are a lot higher. If you do dating apps / online dating you have to accept there's a certain amount of crazy there, and you are rolling the dice with each chick you shag.
Or you could do what this forum member now does, which is video record all his initial sexual encounters. Had he done that in this case he would've had exculpatory evidence and he wouldn't have gotten the sodomy (forced oral sex) conviction he did. Again though, hard to blame him for not doing that. It's a pain to set up secret recordings and feels paranoid. Until, I guess, you need that video and it isn't there. Not saying you have to or should do this... however if you do a lot of high risk dating (dating apps, drunk girls, girls on drugs, feminists, women with personality disorders) you may want to think about setting this up.