Sounds like lateral learning which can be good if well done but it usually isn't well done. FWIW, we skipped a kid who was already the youngest in grade and it was a good choice.
When I've seen "wide" work is when it looks something like this:
The math class is studying shapes and will spiral back to more in this topic in future years. Your child likes depth (mine had this issue with spiraling math curriculum and wanted to learn all about fractions, for instance, not just how to reduce them when they first came up). So, they go wide by teaching her geometry topics like the angle sum theorum or the pythagorean theorum which, in turn, requires teaching some basic algebra, multiplication, etc.
Where I've see it not work is in an instance like this (this is what dd13's 4th grade math enrichment looked like):
Your child knows most or all of the math her math class is learning. So, someone comes in once/week and pulls her and a few other kids out to do suduko puzzles and similar activities.
