The definition of a hypopnea varies a bit, but generally, it's a 50-80% reduction in breathing, with a desaturation and/or an arousal. There is at least some movement, so the BiPAP will be able to pick up effort and respond.
BTW, I agree with Christine that CPAP and EPAP are not the same thing, but in explaining the differences of CPAP and BiPAP to patients, I will often asssociate them very closely, as in:
"You are sitting here now breathing with no support, a supplemental pressure of 0. We are going to add pressure to your airway to inflate and support the unstable airway, for example, to 5 cmH2O. In both CPAP and BiPAP, this becomes your baseline pressure. In BiPAP, however, when you inhale, the machine will give you additional support, adding some extra presssure. This gives you a second level of pressure. The first level, CPAP, becomes EPAP, and the second level is called IPAP. Two levels of support, ergo, Bi-Level."
Sometimes offering the explanation in this way makes it a little more clear.