For all practical purposes, it is a BGA. And you can treat it like any other BGA. The differences are mainly internal to the part and of no real concern to the normal user of the parts.
There are a lot of packages that the different companies call different things-- but are essentially the same. The only things that most users would care about is size, solderability, handling requirements, and heatsinking issues. In other words, what's inside isn't all that important to most people and can be safely ignored.
I suspect that, in this case, the WLP is almost the bare die with balls on it. As in, the balls connect directly to the pads on the die without a bond wire in between. The die isn't completely bare, of course, as there would be a protective coating on the sensitive bits. This type of package is not at all unique to Maxim. TI has some opamps in that package, and I've used some ESD diodes in a 4-ball version.