Thanks to Ancestry there is a simple explanation of the McManus origins.  Since it is very confusing to distinguish clans without knowing the clans actual origin, this provides a map for possibilities.  Niall of the Nine Hostages,  whom we match genetically, apparently suggests some Scottish input.  Note the Roscommon and Fermanagh (for the Irish) is connected with either O'Connors or Maguires.  We are not DNA compatible with Maguires so it appears. The Scots McManus have a different clan name altogether, DNA not studied.  

Possible meaning of the surname McManus Irish:

Anglicized form of Gaelic Mac Maghnuis, patronymic from a Gaelic form of the Scandinavian personal name Magnus. As an Irish name this is found chiefly in Roscommon and Fermanagh and is connected with the O’Connors or the Maguires; in Scotland it is connected with the Colquhouns.  Contributed by Ancestry Family Tree Section.