Anyone else having 4 player only bracket as well?

Looks like you got into a leftover group. If the total number of players in a division can't be divided by 8, then you will have a smaller group like yours with the remaining players. If the number of the remaining players is an odd number, like 5 for example, then 1 player will get a "bye", which is basically full points rewarded for them without having to fight (because there is no opponent available), while the remaining 4 battle it out.