Every strength meter is a model of an attacker, and models are wrong in knowable ways. Worth stating what this one does not capture, because a confident green bar invites more trust than any heuristic deserves.
It cannot know what an attacker knows about you. A password combining your child's name with your house number looks structurally random and is trivial for anyone who has read your social media. This is the largest blind spot in every tool of this kind.
It is not a full dictionary check. The word list here covers the entries that dominate breach corpora, not every word in every language. Something can pass cleanly and still be a common word in a language the list does not cover.
It measures guessing resistance only. Strength does nothing about reuse, phishing, or malware reading your keyboard. A perfect password leaked from a breached site is just as compromised as a weak one.
Where it is genuinely useful is diagnosis rather than scoring. If it names a keyboard run or a leet substitution you did not think counted, that is worth knowing — those are exactly the patterns people believe are clever and attackers try first.
What to do about a weak result
Do not patch it. Adding a symbol to the end of a dictionary word leaves it a dictionary word with a symbol on the end, and the cracking rule that finds one finds the other. Generate a replacement instead — the password generator produces random strings and memorable passphrases, both offline.
And if the account you are protecting only exists to receive one verification email, consider whether it needs to exist at all. A disposable inbox avoids creating the account in the first place, which is the only credential that can never leak.