I just want to add something here, one thing to keep in mind, this couple is from Australia (unless their is another Melbourne somewhere), they have a completely different outlook on sex, swinging ect. ( and I mean this in a good way)Swinging is something that is very common place there and sex is an open subject. Here in this country everyone has to be so discrete and its so taboo.
We have no way to know every detail of their encounter. What their rules were if any. You cant expect someone to write a novel about their first experience and provide every detail. The fact is it's their experience and if it happend that way, and all parties are ok with it then that is great! Just because your rules differ and its a red flag to you doesnt mean that it's a red flag to them. It could mean that they have a great deal of trust in their relationship.....