Crikey, Caernarfon is on my list of places 'to do' next spring and my route will take me straight over Snowdonia. What height were you at and looking back would you have stayed upwind of the hills?
Looking back, with a surface wind of < 5kts at Caernarfon, no I wouldn't have done anything different (why would I?). On the way back, I routed well west over Anglesey to remain clear of any rotor. Caernarfon is a regular run for me and I've never known that before with almost zero surface wind. You can't get there if you stay upwind of the hills in an easterly.
Flying over Snowdon is fine, but I wouldn't do it in high winds or lowish cloud.