Not necessarily. The definition allows biweekly to mean both, because bi- simply refers to their being 2, so it is defined as being “twice per” or “every two”. If it could only be used in the way you present then the word bifurcate would mean to replicate, as opposed to divide in two.

That being said, dictionaries will often note that semi- should be used to avoid confusion, and writing style guides, like Chicago, will state semi- needs to be used for instances where you mean twice a week.