What are you confused about? Did you really not connect the dots? Let me spell it out for you then...
Does anyone know if there is a repo where I can install xdd from?
FreeBSD only has one "repo" and we don't call it a repo. ... multiple repositories for FreeBSD do not exist.
(snip out mindless banter)
Official and possible are two different things.
Your counter to their question was that there is only one official "repo". However, it's absolutely possible to install packages from other "repos".
In terms of terminology, check out this announcement email which shows that the terminology of "repository" and "repo" is part of the FreeBSD parlance. The word "repos" is actually part of the file path used for storing package repository info... which actually makes your previous condescending banter more funny because you're wrong.
tl;dr: It is possible to install packages from unofficial repositories (and OP's original question is perfectly valid). "Repo" and "repository" is also correct FreeBSD terminology.