
Yes, the deer is male because of his antlers. Although it is possible for female deer to grow antlers if they have too much male testosterone, it is very, very rare. And reindeer are the only kind of deer that have have antlers growing for both males and females. Even so, I don't understand why our MC keeps saying that Bai Ze is female just because he's pink and delicate. It could be a translator's error, to be fair, and not the actual author's fault for the continued use of female pronouns for Bai Ze.

If you read through the chapters after Bai Ze told the wolf he was male, the MC continues to use both male and female pronouns for her deer companion. I do believe that's a translator's error. In one of the more recent chapters, the MC refers to Bai Ze as female by saying she/her in her thoughts. It was the chapter where our MC is leading her portion of the army to the "allied" army's camp. MC was riding on Bai Ze and her lover was riding on the wolf.
The wolf and deer relationship is really cute. They so wholesome, they're kinda like the icing of the cake in every chapter. If I'm not mistaken, the deer is revealed to be a male in one chapter, it's still cute how the wolf is still following him though haha