An almost typical story of rise from non league, I have no idea of their history, I presume they had an owner that threw money at it, I doubt the rise was 'organic', I may be wrong though.
Look at clubs that have historically been in the top 4 leagues there's plenty have been down in national league. Some make it back, others don't, it's just the football pyramid, winners and losers every season.
Notts county were a first division club in my lifetime, as were Oldham.
It is was it is.