Why is the answer not subjunctive?

Question

Consiguió mantenerse escondido durante horas ________ dónde estaba.The answer is sin saber los adultos. I’m not sure why the answer is not subjunctive as there are two different subjects, the one who stayed hiding and then the parents

Inma Sánchez · Accepted Answer

Hola Faith
There's a section by the end of the lesson saying that we sometimes use the infinitive: 
"Sometimes, the infinitive (after "sin") is used when the subjects are different. When this happens, the second subject tends to be placed at the very end of the sentence. This structure is a bit more colloquial than sin que + subjuntivo. For example:

Se pusieron a ver una película muy violenta sin estar acostados los niños.
They started to watch a very violent movie while the children were still up. [lit: without the children being in bed]"

I hope it clarified it.
Saludos