It's not. Common vs civil law (i.e. where law comes from) is orthogonal to the roles of the fact-finder and parties in a dispute at trial. Most Americans will be familiar with an adversarial model, where each side's lawyer is making the best case for their side. In Scotland, the responsibility is aligned differently, towards helping the judge to discover the truth.
"In civil law countries, judges are often described as “investigators.” They generally take the lead in the proceedings by bringing charges, establishing facts through witness examination and applying remedies found in legal codes."
"In contrast, in a common law country, lawyers make presentations to the judge (and sometimes the jury) and examine witnesses themselves."
Also, asked my wife who is Scottish litigator:
Most law that is case law but not criminal legislation is civil law. We not have an inquisitorial system system but in practice judges do ask questions regarding legal submissions made by parties.
https://onlinelaw.wustl.edu/blog/common-law-vs-civil-law/
Not sure that Scotland really qualifies as a civil law?
https://en.wikipedia.org/wiki/Scots_law