There's a huge amount of year-to-year variation in goaltender performance.  The general consensus is that save percentage converges to true talent levels after approximately four full seasons, though goaltender true talent is rarely stable for four seasons.

A significant portion of the variation in overall save percentage is variation in short-handed save percentage (and, to a much lesser extent, variation in PP save-percentage.)  If a goalie posts a very high SH save percentage one season, should we read anything into it?  Not likely.  This chart shows the regression to the mean of ES and SH save percentage for pairs of one season and two seasons:

Basically, Even-Strength save percentage, which is measured over a large number of shots, is a significant predictor of future performance, though it must be heavily-regressed to the mean save percentage.  SH save percentage, on the other hand, is essentially random.  Your best guess of next year's SH save percentage is the league average.  Indeed, last year's even-strength save percentage is a much better predictor of next year's SH save percentage than this year's SH save percentage.  No surprises here - lots of shots, even at even-strength, give us a better estimate of a goalie's talent level than a small number at any other strength.