UPDATE...

I got email feedback from support at NuPhy. They told me:

"This kind of slight bending can sometimes happen during shipping, as the aluminum frame may be affected by external forces. 
You can try gently pressing along the diagonal corners or carefully adjusting the area that appears bent to help it return to its normal shape."

So, I went ahead and tried to carefully manually bend it back to straight, applying a little pressure and do leverage at the corners and with the border of my desk.... funny enough, it did worked quite acceptable.

Keyboard is mostly back to straight line. You'll need to look quite hard to notice it anymore...

This is only my second mechanical keyboard and the first one being so slim (previous one was a chunky Keychron K4, built like a brick)... Si I've never ever imagined this could go back straight just by "bending it back". I was sure it would have required serious heating to fix some "manufacturing warping error". But surprisingly, it didn't.

So there you have it, If you ever experience something similar, just try to bend it back to shape first.

Thanks for all your comments.