Opinion is divided amongst medical people as to whether there is a link.
Some have speculated that the increased blood supply demanded by an external haemorrhoid might cause blood flow to be reduced to other nearby tissues and others think that perhaps the body can't always pinpoint the pain precisely and mistakes the tailbone area for the lower back, pain being expressed in both areas as a result.
You probably know about the link between fibre and haemorrhoids, just make sure it is soluble fibre that you focus on, rather than roughage.
Soluble fibre is easy to spot as it expands when soaked, so think dried fruit, porridge, pulses and brown rice rather than bran flakes, shreddies, etc, which collapse when you add liquid.
Soluble fibre keeps waste soft and moist, perfect for a tormented bottom.
I should just add that natural medicine also relates haemorrhoids to a sluggish liver and so if you are very dedicated to the fibre but see few results, do consider a course of Milk thistle complex.