found more info on this bike, and believe it's the one offered at Costco a few years back for $350
It is indeed a freewheel and oddly spaced at 150mm. Here's a snip of someone else's post
I don't know if the 150mm DH standard was ever made in QR. Even if the frame is steel, I wouldn't want to try a 135 or 170mm QR hub. If aluminum, just ride it as is.

Quote: With a 150 mm rear hub, and a 7 speed freewheel (not a freehub) it greatly lacks the ability to be upgraded. This is where the similarly priced Mongoose Vinson excelled. Still, as long as youre not going to upgrade (or break) anything, and only need it for some light duty riding, youre out of options at the price point. Vinsons are hard to come by, and certainly arent selling for as cheap as they did black friday 2015. So you may well be right, youre not going to find anything else for this price. Unfortunately the smarter move may be to hold out until you can push the budget a little higher (Framed / bikes direct)