Top-down and bottom-up development are usually used to mean a from broad scope towards a narrow scope or from a narrow scope towards broad scope perspective on the development of something.
Both terms are sometimes wrongly used as somewhat equivalents of centralised and desentralised development. (You can have centralised bottom-up developments, and decentralised top-down developments as well.)
I think that it possibly means that they need to start from scratch, so they probably need to either re-do everything or they're starting a new business. Although it may mean something totally different depending on what context you use the phrase in. And I believe that MissFit and SpiceMan have accurate descriptions as well. (It's all in how you use it - and it's often misinterpreted...) I hope that this helps you to understand this phrase better!