In all honesty thinking about it it's probably not *that* impressive. That means it had a better May than the 3DS or Wii U had in the US, and 3DS was never really a juggernaut platform in the US, it was fairly rare to ever even see two 3DS games ever in the top 10 NPD at the same time. Wii U ... well uh we know how that went.
And software being up YoY from last year makes logical sense, there were only like 12-15 retail releases total for the Switch this time last year. There's easily much more software available now and the userbase should be double-triple where it was a year ago. Software should be up by double.