In the examples you gave, the brackets indicate that the words within them have been changed from the original — but still means the same as the original. Instead of “he” the person probably used someone’s name and there was a reason not to use the name in the publication.

For example, if in an interview I said “John Smith is a terrible human being. I saw him purposefully steal from a charity jar” the editor may feel that my opinion of John Smith as a person is irrelevant and simply print “I saw [John Smith] steal from a charity jar” and still attribute the quote to me.

Brackets are also used inside a parenthetical expression. (I wasn’t sure you would know this [or anything for that matter] but figured I should tell you.)

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[ . . . ]

see hlods them up just fine

I just use () mostly