Great questions. Bivar is careful in making any general claims about the sword and simply describes it as the sword of state in Kebbi. He mentions that local oral tradition in Argungu ascribes it to Muhammad Kanta Kotal, the founder of the state, and only states that the hilt may be of sufficient age to be compatible with such a claim.
When it comes to the quillons turning toward the blade and terminating in dragon heads, I believe that to be a Timurid feature, in turn inspired by contact with China. Here is a nice Timurid jade quillon block in the Met collection:
https://www.metmuseum.org/art/collection/search/56220
There are similar quillons on some of the Holy Swords of Islam in the Top Kapi treasury. Ucel's opinion is that these date from the late 16th century. With Ottoman expansion to the east into formerly Timurid territory, some of the local craftsmen were relocated to Constantinople and brought those artistic influences with them.
Going back to the two swords in question. The private collection monster head nimcha is dated by Pilz, the catalogue's editor to the first half of the 17th century. This is consistent with other dated nimcha examples, such as those of Dutch admirals, and it makes sense that this type of quillons would have taken some time to get to the Maghreb from Constantinople. When it comes to the "Sword of Kanta", if the dating is similar, then obviously it could not have belonged to Muhammad Kanta. On the other hand, a 17th century dating would be more in line with the broadsword blade. Nothing is absolutely certain, but the signs seem to point toward this sword being a little later than what the oral tradition claims.