Looks screen printed to me, but does it really matter? If you can't tell, the customer probably can't either. How many do you need? If you only need one or two, then screen printing is going to be really expensive compared to a digital print or just laying vinyl.
I have worked with a thin .020 gloss rigid vinyl before (Gill has some in the back of their catalog). It's like a thin credit card material. I bet it's something like that.
What probably more important, is the application, how many you need and whether it will be outdoors baking in the sun's destructive UV rays for years.
If you do need more than a dozen or so, we would love to screen this for you!