It is not a fastmine the way that term is normally used (meaning most of the coins mined in a few months or less, before slowing way down). The Bitcoin mining rate was the same for 4 years, which is not only not a fastmine, but it is slower than that vast majority of new coins.

It is also not an instamine, which properly refers to some kind of malfunction or failure of difficulty to adjust that causes the coin to be mined faster than the specified rate (in fact Bitcoin was mined a bit slower than scheduled in the first year).

However, it is fair to say that was narrowly mined, in that it was mined by a relatively small group of people (though claims sometimes made that it was only "a few" people are probably wrong) for the first year or so. Whether you think that is unfair or represents a hinderance to the success of BTC is up to you. The argument has been made by quite a few people that satoshi's alleged stash is a cloud over the market since he could decide to start selling it at any unknown time.