I believe the SPA card does not use the main IOS image, it needs it's own and that is why you are getting the message about upgrading. Basically when you upgrade your IOS there is an automatic FPD upgrade for any SIP/SPA cards but you need to have the FPD image on your switch. It could be that the card was only added after you had that IOS on the switch.
Have a look at this doc which explains all about FPDs and how to upgrade -
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...