Yes, if you measure inflation by the increase in the amount of money in existence, the first block mined represented an infinite amount of inflation, the second block mined created 100% inflation over 10 minutes, the third block created 50% inflation, and so on. But, if the system functions as designed, this rate asymptotes to zero fairly quickly. You are of course correct that the system may not function as designed.

However, it is more common to measure inflation by the increase in nominal prices of goods, as I did above with gold. And, by this measure, Bitcoin is deflating. It's hard to measure the deflation rate with precision because it's so volatile, but at the beginning of 2011, it was worth 10¢, and now it's US$6600. It's oscillated wildly around the exponential trend line by about a factor of 3 on each side, but the trend line itself is a deflation by about 75% per year (or of 300% per year, if you look at deflation that way.)

Presumably this won't continue forever, as it's more appropriate to tulip bulbs than to a usable currency, but it is certainly quite far from inflation in the usual sense.