Hey now, wait a minute. We can argue all day about kefir, kafir, and kaffir, but don't you impinge on the dignity of the semicolon just because the previous poster used one incorrectly.
I agree that if you think "Wrong root word. You're thinking of Kafir." is acceptable, so too would be the semicolon usage, which is why I said "arguably incorrect" rather than just "incorrect"
"[That is the] wrong root word; You're thinking of Kafir".
Since in the first clause, it seems like the intention is to point to the previous comment that is the matter at hand, which was actually written not just thought about. However, other readings might be possible.
The previous poster’s usage of a semicolon in this instance was, in fact, correct.