I bought a new M&P22 Compact and an M&P Shield 9 yesterday. In the box with the M&P22 was a piece that looked like a backstrap. As far as I know the Shields and M&P22s didn't come with swappable backstraps. I've looked in the user manual and searched online and I can't find any information about this piece. Anybody know what it is?

Looks to be a backstrap from a Walther PPQ



Maybe evidence of S&W making their own PPQ just like they had their own 99.

That would be an awfully odd piece to have fall into my packaging.