That initial instruction is an accident waiting to happen in some circumstances.
The phraseology is all wrong.
The phrase "descend 5000ft" can very easily be misconstrued as some pilots will understand that as - reduce current altitude by 5000ft -
Thankfully at 10000ft, it made no difference which way you interpreted it as either way you were going to end up at 5000ft. However, had you been at, say for example, 8000ft.....then depending on how you responded to "descend 5000ft", you would either have ended up at 5000ft or 3000ft.
It is a problem that I deal with every day over here. And part of the battle is that my boys just don't see the difference. It's the preposition that's vital.