It says I'm underneath so I could be a long way below with oat well above zero degrees but then maybe I am just below and my real temp is negative
and
because my assumption is that drizzle is associated with a stratiform cloud, however it will most likely form between -10 and -20
This is why people run into trouble in exams - they read things into questions that are just not there. The OAT is zero and the visible moisture is drizzle.
The conditions for the formation of airframe ice are met: visible moisture (drizzle) and OAT (skin temperature) zero or less.
Drizzle consists of small droplets, so is unlikely to form clear ice because there's little release of latent heat as the droplet freezes, hence the remainder of the droplet does not remain liquid and flow back before freezing.
Only rime ice is possible.