Yes, you could say it's a closed list of two. Keep in mind, though, first past the post is a closed list of one under those circumstances. But don't mistake the two candidates on the ballot as comparable to an MMP list. The types of list that exist in MMP don't exist in DMP. They're different.
The other thing I'll mention is that was a design choice. I think it's best to keep the intra-party competition in open nomination processes before election day. If the committee decides they disagree with me, you could easily allow people to rank those two candidates.