The number is not 21 million. It's currently 21*10^8 via fractional transactions and expandable (meaning practically and theoretically infinite).
If everyone started talking about cents instead of dollars that wouldn't mean there's 100x as much money... 1 cent would still be worth 1/100 of a dollar.
Likewise, if you started dividing down to 1/1000 of a dollar it wouldn't be inflation. Each 1/1000 of a dollar would still be worth 1/1000 of a dollar.
Edit: and if you suddenly replaced every dollar with 1000 newdollars, those newdollars are also worth 1/1000 of what they were before.
It's currently 21*10^8 via fractional transactions
First, if by fractional transactions you meant satoshis, the math is 21 * 10^14 (21 million bitcoins * 10^8 satoshis per bitcoin).Second, there is no question that Bitcoin is deflationary in the long term. The fact that it can be split in smaller units doesn't change that at all.