I’ll be honest, what’s strange to me is that I’ve never heard anyone who wasn’t a fairly conservative Christian (and not a recent convert) assume that two people who stayed in the same place were sleeping together - at least not if they hadn’t already made that assumption. They’re much more likely to assume a boyfriend and girlfriend are sleeping together, but even then I’ve found this is a defeasible assumption based on what they know of the couple.
It’s interesting how many conservative Christians claim to be disgusted by “the secular culture sexualizing everything” yet they too often sexualize what are not inherently sexual activities such as sleeping in the same building. Or even spending any more than 5 minutes “alone” together without a chaperone. Yet as I mentioned before, even the Duggars and Bates have no problem with a significant other staying in the same house, as long as there are chaperones around.
There was even a recent “Bringing Up Bates” episode titled “Bobby’s Moving In” though I do suspect the company promoting the show chose this slightly scandalous title, not the Bates themselves. Bobby didn’t actually move in with the Bates, he just moved to the same town as the Bates daughter he is courting.
The assumption that an otherwise chaste couple would now be sleeping together in virtue of spending the night just doesn’t seem to be that common, especially if they were in separate rooms.
I think there is more of an understanding in secular culture that just because a man and woman spend time alone together doesn’t mean they’re having sex. Indeed, even couples who ARE “living in sin” aren’t usually having sex every single night, no more than married couples - and I’ve read stats that married couples actually are more frequent about sex on average than non-married ones.
All that being said, I don’t think the issue is just about “how far can you go before you fall into sexual sin”, I think you could certainly make a case that sleeping in the same bed together is way too far to go in terms of emotional closeness than a couple who isn’t married should go.
Ironically, I also think this is the case for courting models that demand the courting couple become great friends with the parents and siblings of their intended, I think this can also lead to premature emotional intimacy, and put pressure on the young couple to continue the courtship into engagement and marriage, just so they won’t disappoint all the family members involved.
I’ve even seen courting literature recommend the young men to “court her father first” and that’s squicky in a lot of ways.

It seems much of the “court her father” advice is based not just on the idea that the father is a gatekeeper who filters out men who are obviously not good marriage material, but on the patriarchal assumption that “if her father likes you, he’ll justly use his parental influence and authority over her to make her accept you” as if the actual preferences of the woman herself are irrelevant, and she’s just a piece of chattel to be given by the father to her husband.
It strikes me as similar to someone who has children, introducing them to potential suitors way too early in the relationship.