This question is similar to this one pertaining to Mace Windu's assessment, but there are different circumstances that I think are noteworthy, and therefore justify a separate question. When Mace Windu explained his conclusion to Yoda, they had now seen what Darth Maul was capable of, as he had fought two Jedi, and successfully killed one of them (a very well-experienced Jedi Master).
However, when Qui-Gon first fought against Maul, it was the first time that any Jedi had seen him (at least as far as what the films show; and none of those present during Qui-Gon's subsequent meeting with the Jedi Council had any prior knowledge of Maul), and Qui-Gon spent very little time fighting against him at that point. When Qui-Gon escaped by boarding the Queen's ship, he had this exchange with Obi-Wan:
OBI-WAN : What was it?
QUI-GON : I'm not sure... but he was well trained in the Jedi arts. My guess is he was after the Queen...
And later, when he relayed his experience and his conclusion to the Jedi Council:
QUI-GON : ...my only conclusion can be that it was a Sith Lord.
KI-ADI : Impossible! The Sith have been extinct for a millennium.
MACE WINDU : I do not believe the Sith could have returned without us knowing.
So, considering the Council's skepticism of Maul's affiliation due to how long the Sith have been absent from the Jedi's affairs in the galaxy (and thought to have been long-extinct), what was it that led Qui-Gon to believe that Maul was a Sith Lord? I understand that it was probably easy to conclude that he wasn't a fallen Jedi, but why not some other type of Dark Jedi? The definition of Dark Jedi (at least according to Wookieepedia) is a Force-sensitive that adheres to the Dark Side, but isn't a Sith. In fact, if we rely on Legends, there were a few notable examples of Dark Jedi, such as Allya, then there was Kibh Jeen during what became known as the Dark Jedi Conflict, and, most notably, there was Qui-Gon's former Padawan Xanatos. And, on another note, Maul was a Dathomirian Zabrak, not a Sith Pureblood.
Based on what Qui-Gon knew at the time, wouldn't it have been the more logical to conclude that Darth Maul was actually a previously unknown Dark Jedi?
Note: While I drew upon Legends information in forming my question, an answer from either Canon or Legends is acceptable (depending on what information is available). If possible, answers for each are appreciated.