If you think it was an accident, what is your explanation for them being out at 2am on a Tuesday, especially given they're quiet homebodies?
In answer to your question- we really do not know that they were actual homebodies. Their family members in another country far away thought they were. That doesn’t mean they didn’t regularly stay out late or go out late at night on occasion.
Obviously they did go out late on the fateful night they went missing.
There may have been other weeknights when they took late strolls or went out for a late night snack. Maybe they did this regularly or maybe only a couple of times a year.
Aberdeen is considered a safe city. Europeans/ ladies alone or with friends (depending on the city) often walk late at night with no fear - unlike cities in the US.
Along the next bridge over (Wellington Road) there are several “all night” places open including a coffee shop and an all night grocery/ sundry store. (Londis & Wild Bean Cafe)
Another poster mentioned her late night searches for chocolate and such- it was a great post.
They could well have gone out for a late night stroll to get a snack or something one of the sisters was craving.
I think that this was an innocent adventure that ended up with some confusion on the parts of the girls and a tragic accident after they took a wrong turn and one of them took a fall and the second sister was unable to rescue the first.
Maybe they had been drinking before they went out. Maybe they simply were confused as to which area they were in after they were walking and talking for a while. They apparently only had one phone with them but maybe they didn’t pull it out to navigate the streets.
I just think that a tragic accident happened.
They may have been confused after crossing the Victoria Road bridge when they were intending to be one bridge over in the Wellington Road area for their snack/ errand.
All imho