Hello,
OEM license is always bound to the motherboard, and like you said, manufacturer put it there.
As for the digital license you saw, digital license doesn't conflict with OEM license. It is the format of the license, not the type. OEM license can be digital or non-digital (back in the days). Retail license can be also digital or non-digital. For your case, this doesn’t mean that your Microsoft account “owns” or “contains” the license the way an online purchase would. It simply means your Microsoft account knows that this device has a valid Windows license, so if you replace some parts (like the hard drive) but keep the same motherboard, you can reactivate easily.