They do not mean the same thing:
4 in 4000 stands for 4 thousands
4 in 400 stands for 4 hundreds
In this case:
[tex] 4 438 = 4 \cdot 1000 + 4 \cdot 400 + 3 \cdot 30 + 8 [/tex]
You can see, that first '4' means 4 000, while the second one means 400, so the first one is 10 times greater.
