It is a common method by intelligence agencies to use such groups, ie jundallah.
What prior actions did they take that terrorized the populace they are trying to win over and free from the Mullahs?
To clarify, "Jundallah" (the one which was headed by Rigi in Iranian province of Sistan-Balouchestan, not in Pakistan) has never been a "terrorist grp".
As allmendream said, they have always been against the mullahs' regime, and conducted operations against Regime officials, such as members of IRGC. They were actually formed in 2002.
Although you're right about MeK/MKO. They do have a history of "Terrorism" (per allmendream's explanation) dating back to the Shah's era. They also have a history of actively supporting Khomeini & his rise to power, until afterwards when Khomeini refused to share power with them & indiscriminately executed a large number of them.
Unlike "Jundallah", MeK/MKO has always been an ideologically-driven group (not a tribe). Their philosophy (ideology) is a hybrid of Islam & Marxism. They act as a cult (Unlike Jundallah). However, in the last decade, they too have only targeted regime officials, are fighting the Mullahs' regime, not aiming to terrorize the populous.
"Jundallah" (in recent yrs known as "The Iranian People Resistance Movement"), has repeatedly & publicly said:
"The Resistance condemns torture, murder and execution of its members by the Islamic Republic regime. Many have been imprisoned and executed without trial. The Resistance leader, Mr. Abdolmalek Baluch [Rigi] stressed that while Iranian People Resistance Movement believes in peaceful resistance, its demands for equal rights for all Iranian natives and religious minorities have gone unanswered and the regime has resorted to the most barbaric forms of torture and executions. The Resistance, therefore, has no other recourse than to counter the regime militarily. The world should know that the terrorist Islamic Republic regime has treated the natives of Baluchistan with utmost cruelty and has denied their basic rights. Tribal people are imprisoned and tortured for no reason, other than to terrorize and oppress. The Iranian People Resistance Movement has no relationships with smugglers, Taliban or Al-Qaida and is a member of the joint tribal resistance, also consisting of [Iranian] Lor, Bakhtiari and Qashqai tribes. Our demands are rational and legal. Our basic demands are regime observation and respect for our rights and religious freedoms as declared by the UN Human Rights Charter." -- see #26 here
It is typical of the mullahs' regime to accuse everyone else of terrorism, when they are the real deal terrorists, by any definition of "Terrorism".