Translation:Because it was scary, I cried.
Katta is the past-tense form for adjectives (at least i-adjectives; I can't remember if it's for na-adjectives as well).
It sounds foreign because we don't have adjective tenses in English. We have to say it was scary, because we don't have a single word for scary-in-the-past.
Practically, "It was scary" makes more sense as an English translation.
In English, we make the distinction as a matter of course (we like subjects). But in Japanese, a more contextual language, that subtle difference doesn't change the Japanese tendency to use 怖い (こわい). In 15 years, I've never heard anyone say 怖じる.
I feel like the answer should also accept other pronouns such as 'he cried' or 'she cried' in place of 'I cried'.
The passage 'こわかったから、なきました' never explicitly indicated a first person point of view so its just as likely the subject here could've be someone other than myself.