Here is an interesting article for anyone like me, who has watched an interpreter on the ABC news doing simultaneous translation into AUSLAN and wondered how they do it - fascinating.
Answer: they make it up as they go along! (not really, read the article).
Whereas for translations into other languages you have to find another way to say something you don't know the word for ("an operation where they drill through the skull..."), in the example quoted here the translator made up her own sign to symbolise the operation in question.
Now the article does not definitively say there were no deaf people in the audience watching this and thinking, What the hell...? So we can't be sure that's not the case. But it's a very interesting read which makes the case that there is, after all, something quite different about sign language compared to spoken languages.
There seems a lot more flexibility (or perhaps just different type of flexibility) and for all we know that sign language has grammar and structure there is also obviously a lot of what I would call "pictograms", which is what allows people to insert their own idiosyncratic or ad hoc signs and others to understand them.