This is not a debate sub. I would suggest you post this on s/GCdebatesQT instead, and please take a look at the rules on our sidebar.

Why would a trans man with this same neopenis not be a man and their neopenis not be considered a penis?

Because:

• There are only two types of gametes involved in human reproduction-- sperm and ova. (If you have discovered a third type of gamete, please contact the press and collect your Nobel prize.)

• There are, correspondingly, two sexes found in humans-- one that has a reproductive system corresponding to one type of gamete (sperm), and another that has a different reproductive system corresponding to the other type of gamete (ova).

• The two sexes are called "male" (for humans with a reproductive system corresponding to sperm) and "female" (for humans with a reproductive system corresponding to ova).

• Transmen are female, by definition-- they are female people who "identify as a man" or otherwise as not having the sex (male/female) that they have had from birth.

• Attaching an external appendage to one's body, i.e. a "neopenis", does not change one's reproductive capacities. (edit: i.e. whether one has a reproductive system corresponding to one type of gamete, sperm, or the other, ova.)

Sometimes people ask, "Why are these discussions about man/woman so focused on reproductive capacities?!" and the grand answer is that it's because... biological sex is defined on the basis of reproduction (i.e. gametes).

Hope that helps. Again, this is not a debate sub and you might want to try posting elsewhere.