You're right that the second sentence is simpler, but both of the sentences are in the active voice. (The difference between the two is in verb tense: the first sentence is in "present perfect" tense and the second sentence is in "simple present" tense. The first sentence places more emphasis on the writing as a completed action than the second sentence.)
A better example of the passive voice here is "A comment on HN was written by me".
A better example of the passive voice here is "A comment on HN was written by me".
Here's a guide to the difference between passive and active voice: https://writingcenter.unc.edu/tips-and-tools/passive-voice/
...and a guide to verb tenses: https://learningenglish.voanews.com/a/introduction-to-verb-t...