First, your version is past EOL. You should upgrade to either the latest version or the current LTS at your earliest convenience. Your upgrade path is:
8.3.1 → 8.9.2 → 9.0.1 (last step optional)
Regarding your actual question, the rule to detect commented-out code blocks works on heuristics. I can’t tell you what word(s) in your example triggered the issue but this rule is imprecise by it’s nature.