Their rendering method for this does sound quite interesting and may be well worth it.
However, be honest and transparent about it. If you don't render every imagine in "fresh" 1080p but rather use some approximation methods that provide better performance for a somewhat acceptable loss of quality, fine. But when you're adamantly talking about resolution and stuff in the first place, then tell us what's exactly the case in an interview or s.th. else before launch.
I don't think calling it native 1080p is really appropriate when not only certain aspects of the visuals (like the mentioned lighting for example) but all the pixels themselves are affected by these round-about solutions.
Now I do understand that this stuff is rather in depths and telling the community it isn't native 1080p will immediately create much worse PR. Yet, I'll take underselling over overselling any time of the day. If you know what you're doing is better than e.g. upscaled 720p or 900p then give some tech site or so an interview about that. Those customers who can understand and value that stuff will be happy to spread the information. In the long run, that's how a company gets my respect. As opposed to retrospectively saying "yeh, well... I guess it's not 100% native 1080p, ya know?!"