Naticle, the term anal being used to describe someone who is ridiculously obsessive about something comes from the work of psychoanalyst Sigmund Freud. Freud argued that, as humans developed, they become fixated on different and specific objects through their stages of development—first in the oral stage (exemplified by an infant's pleasure in nursing), then in the anal stage (exemplified by a toddler's pleasure in controlling his or her bowels). So anyone who is obsessive or controlling in nature gets described as anal!
Hope that clears that one up :-)