Good question, the personal testimony of the caller in question, traumatised as he may have been, matches what numerous eyewitnesses (including firefighters present on the day) have described ie explosions being responsible for the collapse of the buildings, pointing to the fact that they were planted prior to the towers being hit. Furthermore the cars surrounding the towers exploding also suggests the use of DEWs. Check out the link below and the videos as well which corroborate the caller’s account.