PCs declined, but Intel basically ripped AMD's throat out to achieve its unit increases. Expect it to get worse for AMD as BYT-M ramps.
I don't think MSS gains against AMD is sufficient to explain the swing from double-digit decline to 3% growth. Not unless Intel were to take nearly all of AMD's sales - but AMD only reported about a $100M revenue decline. While this represented about 12% of AMD's PC product revenue decline, that same $100M is about 1.2% of Intel's PC group quarterly revenue.
Besides, if you look at Intel's ASPs vs. AMD's there's a conversion factor of 2:1 or 3:1 between money and units. In other words, $100M may be 2 million units for AMD ($50 ASP) - but it might only be 1 million units for Intel ($100 ASP). I made up the numbers, by the way, just to illustrate the point. I'm not sure what the ASPs are at these days, but it was near these levels several years ago....