I used the bronze speedy spark plug as well. I noticed that while using the bronze version, you get credit for both bronze and silver versions at the same time. The silver version seems to not be linked to any program. So I assume it's just a bug where they linked the silver program progression to the bronze version. I was actually able to complete the silver program with the bronze version still equipped.
Also, you probably got the silver rewards while using the bronze version. I looked back and noticed I was getting packs and rewards for both the bronze program and the silver program while using the bronze program. I was at like 80% done with the silver program when I got to 100% on the bronze program and had been getting the rewards for both programs the whole time.