I'm not wedded to the number, nor do I take it as absolute. However, if we consider that the number represents about 00.50% of all Muslims spanning the globe, it is not that huge. 50 basis point deviation from the mean in any group (although Muslims are not homogeneous) is not that much.

Yes, how did he come up with the number? What degree of radicalization are we speaking of? When putative jihadists claim to be "willing" to take up arms, do they intend to do as they say?