Ron Rosenfeld wrote:
ATC gave you a new altitude to "maintain" until established. That is your
altitude assignment. In my part of the world, it is usually preceded by a
"climb" or "descend" but I don't know if that is required.

I'm reasonably sure that the "descend" is a required part of the
phrasology. But, the real point is that whether saying "descend" is
required or not, controllers are human, as are pilots. On both sides of
the mike, minor mistakes are made all the time. The key to making the
whole system work is to ask for clarification whenever you're not sure you
understood what the other person said or meant.