The Grendel designer was George Kellgren, who is the founder of Keltec, so that’s a pretty natural evolution.
As far as whether it’s a copy…well, the pmr30 was a semi auto poly framed 22 mag pistol with a 30 round magazine. It was pretty unique on the market. S&W, who has recently come out with at least 2 other homages to Keltec products, brings out a semi auto poly framed 22 mag pistol with a 30 round magazine. While not a direct copy it does bear certain similarities that definitely would potentially bring one to think there may have at least been some inspiration taken from Keltec.
Doesn’t bother me though. I like having options, and while I haven’t had any problems with any of the Keltec products I own some people have and to me there’s nothing more frustrating than a product that has an amazing concept but a crappy execution. If you liked the PMR30 but not the manufacturer, Smith now has your gun.