After the Twins' awesome come-from-behind win in the 9th inning against Chicago on Sunday 7/18, Dick Bremer said it was the first walk-off victory for the Twins at Target Field. This was repeated in all sorts of print media and on the TV news.

However, I don't think this is true. As my dad pointed out (because he was there), the Twins won in the bottom of the 9th inning against Detroit on May 4. It was a walk-off wild pitch by Ryan Perry. The only thing I can think of is that somehow a walk off wild pitch doesn't count because it's not an offensive play. However, it is an offensive play because JJ Hardy still took advantage of the situation and ran home. Also, googling "walk off wild pitch" returns 48,000 results. Finally, the walk-off victory against Chicago was also due to an error. Technically, it wasn't a walk-off hit by Young, but Cuddyer's capitalizing on a throwing error. 

Can anyone give me any good reason why 7/18 was a walk-off victory for the Twins and 5/4 was not?