It sounds as if the previous user's logoff was abnormal for some reason or possibly you were seeing the result of someone's failed logon attempt, but that is pure speculation on my part. In any case the probability you might have have caused damage to another student's files is extremely small, approaching zero. Your concern for the integrity of the other student's files is commendable. It would be wonderful if all computer lab users were as considerate as you.
FWIW the only time you need to appologize for your use of the English language would be in the event of using obscene or objectionable material and that is true no matter what language is used. It is a safe bet your English is far better than my command of your native language no matter what it is.