I'm not sure if that's why, but... =それが理由なのかは分からないけど...
例:
・It was raining like crazy last night! I don't know if that's why, but the streets were empty this morning
(昨日の雨はすごかったんだよ!それが理由なのかは分からないけど、朝街に誰も居なかった)
They may be totally unrelated, but... =全く関係ないかもしれないねど...
例:
I wonder if Tom's suddenly in town because his ex girlfriend Laura just got divorced. They could be totally unrelated events, but I smell something fishy...
(トムが急に街に戻って来たのは元カノのローラが離婚したからかな?全く関係ない出来事かもしれないけど、何か怪しいな〜