No, the title is not a typo. While all Islamists are Muslims, not all those who help Islamist terrorists need be Muslim. A number of such cases have come to light over the years, in which non-Muslims aid and abet violence. Cases that come to mind include individuals of Christian, Jewish, and Hindu background:
Yehuda Abraham: A New York jeweler of Jewish origins who pleaded guilty in 2004 to operating an illegal money-transferring business to provide terrorists with shoulder-fired missiles.
Lynne Stewart: An extreme leftist lawyer of Christian background who was found guilty in 2005, of, among other things, "providing material support" to terrorists, specifically the blind Egyptian sheikh, Omar Abdel Rahman.
Tomer Grinberg: An Israeli of Jewish background who pleaded guilty in a U.S. court 2005 of exporting sensitive military equipment to Hizbullah.
Hemant Lakhani: An Indian of Hindu origins and resident of London who was found guilty in 2005 of trying to sell 200 shoulder-fired missiles to an East African terror cell.
Tali Fahima: An Israeli of Jewish origins who pleaded guilty in 2005 to lesser charges; the real accusations was that she helped Zakaria Zubeidi, a Palestinian terrorist leader, by translating Hebrew for him, serving as a "human shield" for him, and other functions.
Michael Curtis Reynolds: A leftist from Wilkes-Barre, Pennsylvania of Christian origins convicted in 2007 of attempting to provide material support to Al-Qaeda and related charges.
Comments: (1) It's generally the far left that sympathizes with radical Islam to the point of joining in its violent actions. (2) Three of the six examples above involve individuals of Jewish origins. (March 28, 2009)
Michael Katz: Sentenced to a year and a day in jail for "attempting to provide material support to Hizballah in the form of approximately 1,200 Colt M4 Carbines (machine guns)." Katz is 68 and a vendor in flea market goods; his name suggests he is not a Muslim but his religion is unknown. (July 14, 2010)
Dino Bouterse, 41, son of Suriname's president.
Dino Bouterse, 41, son of Suriname's head of state, Desi Bouterse assisted in the formation of his government's Counter-Terrorism Unit. Today he stands charged by U.S. authorities of "attempting to support Hezbollah," the Lebanese terrorist group. He has been sitting in a New York jail since Aug. 30. (November 8, 2013) Mar. 10, 2015 update: Bouterse pleaded guilty and was sentenced to 16¼ years in U.S. prison for attempting to provide material support and resources to Hezbollah, along with narcotics trafficking and firearms offenses. The Department of Justice press release explains:
In exchange for a multimillion-dollar payment, Bouterse agreed to allow large numbers of purported Hezbollah operatives to use Suriname as a permanent base for, among other things, attacks on American targets. In furtherance of his efforts to assist Hezbollah, Bouterse supplied a false Surinamese passport to a purported Hezbollah operative for the purpose of clandestine travel, including travel to the United States; discussed heavy weapons that he could provide to Hezbollah; and instructed the purported Hezbollah members about how Hezbollah operatives, supplied with a Surinamese cover story, could enter the United States.
The press release then goes into detail about the plot.