But does the claim that Boko Haram is not Islamic hold up to scrutiny?

Boko Haram and the Dynamics of Denial

It is a common refrain of pious Muslims in the face of atrocities done by other Muslims in the name of Islam that Islam must not be shamed. Whenever an Islamic atrocity potentially dishonors Islam, non-Muslims are asked to agree that ‘This is not Islamic’ so that the honor of Islam can be kept pristine.