There is no way to be certain without taking it apart. However, hopefully, they used dowels and some good glue. It looks like solid wood rather than veneered mdf or similer. That means that the doweled joints (if they are) will be pretty strong.
I forgot about dowels, I couldn't see any screw holes and assumed it was just glued together. I've done stuff like this in my young years and they never heldThere is no way to be certain without taking it apart. However, hopefully, they used dowels and some good glue. It looks like solid wood rather than veneered mdf or similer. That means that the doweled joints (if they are) will be pretty strong.
Really, I almost want to make one just to see.There are a number of different ways that could be put together which would hold up well. Unless someone sits on it I think it would be good.
I don't see any structural issues with it. The weight of a few magazines or books isn't enough to cause a joint failure.They supposedly sell this on Amazon although I can't find it, but it doesn't look like it would hold together very long.
WOW, That looks great! I like it. 👍My son made a simple version of this with mitered corners and used splines to reinforce the joints. I made a similar one from 1¼" plywood and pocket screws.