Inflation - by definition is related to increase in price and reduction in purchasing power
Deflation - by definition is related to decrease in price movement and increase in purchasing power
Factors
Money supply
Demand
Purchasing Power
Price
USD
money supply - increasing
demand - high
purchasing power - reducing
price - increasing
Conclusion: USD is inflationary at current levels
Bitcoin
money supply - decreasing & limited supply
demand - high
purchasing power - increasing
price - decreasing
Conclusion: Bitcoin is deflationary at current levels
Why is price decreasing? Because 1 bitcoin today can buy more USD than it could 1 year ago. Don't convert BTC - USD to perform inflationary/deflationary evaluation, use its purchasing power and unit value.