From what I can tell bump steer isn't much of an issue on this car even when going lower than what springs offer. I've measured the rear and I'm confident that's relatively non-problematic, especially at reasonable ride height changes offered by most aftermarket lowering springs just like RCE Yellows.
I don't know how the front acts precisely but I believe you're feeling what @
wparsons speculates, normal steering feedback from a sports car on a rough road. Real bump steer is when the wheel changes direction due to suspension travel regardless of your steering input (or out of your control like the rear on an AP1 S2k or NC Miata)