Empty cell, no formula, no Macro, no formulas referencing cell - Automatically fills up wi

[Tom_Takula]

I really hope someone understands how can this work (file attached).
So, cell is empty in Col A (like A7), and when numbers are entered in all cells B7:E7, excel copies formula from cell above (B6).
At first I thought - right, easy to do with VBA, but... There are no macros, nothing in worksheet code, there are no custom functions, and now for few hours can't figure out how is Excel doing this. It is not tables, I can tell that (red one similar post).

Also, try deleting A7 to E7 contents, and then enter numbers again in B7 to E7, A7 gets formula from cell above automatically. I copy/pasted whole range to another Workbook, and it works too.

This looks really cool, the only thing is I can't understand how it works and how to replicate it.
Any feedback or thinking would be appreciated,
Tom