Both Foro and Fora are registered at NameCheap, which leads me to believe XenForo owns the domain name and picked it up on a drop as they are registered years apart. It's not too uncommon for defensive trademark registrations (google, gooogle, g00gle, etc. you'll see they own probably 100 variations).
In this case, it doesn't make much sense because Forum, or Foro, is masculine in Spanish while Fora is feminine, and not the right word.
However, Foro and Fora both could be confused with the "radio test" (how the name sounds when spoken), and with a worldwide Spanish-speaking audience, they could get confused that's it's Fora, even though knowing their language, just not quite knowing whether it's masculine or feminine as it's the first time they've heard the word. And, a lost customer.
A hypothesis on it...