Kneeboot

With savings interest increasing, I calculated my non ISA savings interest for the last financial year to see whether I was approaching the requirement for self assessment. My interest was in the region of £ 5000 and so well below the £ 10000. However I logged into Gateway for the first time and found that I am registered for Self Assessment with a unique identification number. In the past I have never been asked to complete a form, never received a penalty for not doing so and have received a tax code notification. Is it normal to be registered in this way or is it something that I should be concerned about ?