There's a difference between multi-entry facilities and single-entry ones.
The former is a facility that can be used by several people at the same time and is typically single-sex. If it isn't then this becomes a multi-sex facility, where bpth sexes may use the facility at the same time.
The latter is a facility that can be used by only one person at any one time and is called unisex because while members of both sexes can use it, only one sex at a time uses it.
In my university and school days, I was in both shared single-sex and mixed-sex flats with unisex facilities and single-sex dorms with single-sex facilities as well as at the end mixed-sex dorms. By far the worst for privacy and safety were mixed-sex shower rooms with flimsy curtains and shared toilets in the latter.
As for today, two of my kids had the former setup at two different university towns (UK). The norm there for university accommodation are 3 to 6 bedroom flats with the residents of each individual flat sharing one or two single-entry unisex bathrooms. With lockable doors.
Even though these bathrooms are safe and private, every student also had a choice between single-sex and mixed-sex shared flats.
What that student describes is not the single-entry unisex bathroom that is the standard* option for UK university accommodation but a multi-entry mixed-sex facility. And it doesn't sound like any of these kids had a choice.
*En-suite bathrooms are the premium option - if they are available at all.