Why does IsNumber find numbers and text?

Question

In any column of data, rows x onwards contain text (column information), rows x+n onwards contain numbers (column data).

I'm using Column B to find (x) and (x+n) using IsEmpty and IsNumeric:

FR = IIf(IsEmpty(.Range("B1")), .Range("B1").End(xlDown).Row, 1)

DR = IIf(IsNumeric(.Range("B1")), .Range("B1").End(xlDown).Row, FR)

IsEmpty returns the right number (x), but IsNumeric returns the same value (x) instead of (x+n).

Why is IsNumeric recognising text as well as numbers?