Here’s a try at clarification. Any oil can be called semi-synthetic if there is a very, very small synthetic content (say 1% or less), or it may have a much larger synthetic content. The percent content does not have to be displayed on the bottle. My understandng is that there are no real standards for content, for semi-synthetic. There are even arguments about whether some synthetics should be called synthetics, based on their base stocks. .
As to their second comment, I interpreted what they said was about API classification, which can be met with selected mineral oils, as well as synthetics or semi-synthetics. API classfications cross all oil types.
All of that said, you still have to meet the oil requirements as specified in the owner’s manual during the warranty period… In many cases (BMW & VW comes to mind), only synthetics meet their standards. In my case, that means I will run a synthetic oil while my Subaru is under warranty (Subaru highly recommends this, but does not clearly specify/require a synthetic). Then I will choose whether to continue the regimen, or not. For the most part, I am running synthetics or semi-synthetics anyway, based on my oil choices for my other vehicles.