"Sufism is a strand of Islam that eschews materialism and emphasizes the inward search for God. Sufi adherents are responsible for some of Islam's most famous and beloved literature, including the poems of Rumi. Followers promote values such as tolerance and pluralism.
Sufi believers can be Sunni or Shiite, though the majority of Sunni. They see Sufism less as a sect than as a way of being, a set of beliefs and practices that lead followers closer to God. “It is nothing more than the spiritual dimension,” Imam Feisal Abdul Rauf told the New York Times. “It is Islam, but we focus on meditation, on chanting sessions, which enable the Muslim to have his or her heart open. The myths people have about Sufis are analogous to the myths people have about Muslims.”" Washpost
"Salafism is associated with literalist, strict and puritanical approaches to Islam. In the Western world it is often associated with the Salafist jihadism  Sufism is associated with the use of prayer, music, dance and the teachings of Sufi masters—who may serve as an intermediary between God and humans—to achieve a spiritual sense of the meaning of God.
While there are Muslims who believe that Salafism and Sufism "overlap", the "standard" Salafi response to Sufism has been called "polemical". According to various observers, Salafists have been "usually ... unrelentingly hostile to devotional Sufi practices", arguing that Sufism is "irreconcilable with true Islam", and one of the elements "corrupting" modern day Islam. Relations between the two movements have been described as one with "battle lines drawn", or a "rift" found in "practically every Muslim country", and in "the Muslim diasporic communities of the West" as well." wiki
"Sufis were characterized by their asceticism, especially by their attachment to dhikr, the practice of remembrance of God, often performed after prayers. They gained adherents among a number of Muslims as a reaction against the worldliness of the early Umayyad Caliphate (661–750) and have spanned several continents and cultures over a millennium, originally expressing their beliefs in Arabic before spreading into Persian, Turkish, and Urdu among dozens of other languages. According to William Chittick, "In a broad sense, Sufism can be described as the interiorization, and intensification of Islamic faith and practice." wiki
The great Muslim scholar al-Ghazali successfully devised an argument for reconciliation between the intensely personal devotion of the early sufis of the Abbasid period and the pietist, scripture obsessed majority who wrested control of the caliphate from the Mu'tazila faction of scholars. The Mu'tazila argued for what might be called an adaptationist understanding of Islam in which the Gate of Ijtihad (new understandings) would never close. The Mu'tazila had been the dominant force in Sunni Muslim thinking during the reign of several caliphs but were bested politically and lost all influence.
Having accomplished this the pietists turned their attention to the sufis of the day. There was a great persecution in which sufis were crucified, burned alive, dismembered alive and so forth. al-ghazali stopped this by successfully arguing that the claim of the sufis to know and experience God was not blasphemy as the pietists insisted but rather was a description of experience of the reflection of God's nature in his creations. (Reflection of a lamp in a window, etc.) This made sufis tolerable to Sunnis in general. (They were almost always tolerable to Shia muslims)
Now the wahhabi salafi takfiris have revived the persecution of the sufis. My SWAG would be that this congregation were of the Shadhili tariqa. They are numerous in that part of Egypt and many of them are of a beduin tribe who understandably has resisted the IS devils. There will be more abominations like this.
If my explanation does not satisfy specialists in these phenomena I can only say that I am not writing for them. pl