I want to start by being clear: calling a wine weird in the world of insipid, mass-produced dreck is not an insult. If anything it's a compliment, a nod to a winemaker who's willing to experiment and take chances and do all the risky things that likely make no financial sense, but can result in bottles of wine that the drinker actually remembers for more than 20 minutes after they're gone. So in that case...this wine is supremely weird.
Let's start with the region. Lazio is the Province of Italy where Rome is located and while that means they have a long history of making wine, for the most part the region has been left behind in the Italian wine renaissance of the past half-century. The most famous wine is the slightly frizzante Frascati, which is one of the world's great cheap and cheerful wines, but has so fallen out of favour that the BCLDB doesn't carry a single bottle. In fact, other than this wine, there's only two other wines at the BCLDB that are from Lazio: a Cesanese (an indigenous Lazio grape), also from Casale Del Giglio (and also weird in a good way) and a hulking 2L bottle of Castelli Romani, which is $15 (approach with caution and Advil).
But things get even more bonkers with the grape. Petit Manseng is a lesser known French grape grown in the South West (and a bit in the Jura). At one juncture it was hoped that its thick skins would produce a full-bodied white that might rival Viognier, but given that I assume you've never heard of Petit Manseng, that gives you an insight into how that gambit went. It's Wikipedia page suggests it holds some promise in planting in Ohio, which is never a good thing.
So with two rather steep barriers against it, the odds that this wine should work are... not good. You can imagine, then, what a unreserved delight it is when it turns out to be such a charmer. It's got a very deep, yellow hue like an aged Verdicchio, and on the palate it's got a wonderful slaty and nutty dance going on, but with a streak of acidity running though that keeps it from being oafish. If you love the complexity of Parmigiano cheese I think you'd be utterly charmed by their weirdo... and I mean that in a good way.