Insofar as you take it for what it is, yes. However, all it tells you is that at that moment in time, at LEAST the number of cabins shown were available. There may be cabins not shown in available inventory but that don't actually have pax assigned yet, either. There are several reasons that this may occur.
So assuming you could book any of those 58 cabins, while you can't say how full the ship will be, the fact that x cabins are available tells you that at that moment in time, it can't be any more full than ((available - x) / available) percent full so far.