This is good news (sort of) - it means hardware filtering is working with your card
It may be that the image(s) you are displaying are still a tiny bit larger than FPV Pro's window surface, and that some slight rescaling occurs nevertheless?
If the images are even 1 pixel larger than the window some scaling needs to be done and the filtering kicks in to smooth edges and reduce visible scaling artifacts.
While effective when making significant size reduction, the filtering effectively blurs the image a tiny bit and the result might be perceived as somewhat unsharp when the rescaling was minimal, say a few pixels (depending on the image's content, more obvious if you have things like text elements or sharp edges in some images, and almost invisible on others).
The filtering method is different between the software and hardware modes, so it is conceivable that a difference can be observed between non-GPU and GPU accelerated mode.