I personally haven't heard of the happening, but a quick AI search shows it's a real possibility. See following:
"While alcohol, specifically ethanol, is sometimes listed as an ingredient in vape products, it is also frequently found as an unlisted ingredient in e-liquids. Studies have shown that many commercially available vape juices contain ethanol, and some contain more than 10%. A study published by VCU News found that out of 56 samples, all but three contained ethanol, and 11 contained more than 10%. "
Unfortunately, I don't think you'd have a strong legal case, just as you wouldn't have a strong legal case for a potentially positive urine from fermented food such as saurkraut, vinegar, or overly ripened bananas where potential alcohol content may not be listed.