My policy, as someone who edits a lot on many Stack Exchange site.
Fixing grammar and spelling errors is good. Your correction of the spelling of different was a valuable edit and should not have been rejected. The reviewers were in error.
Miscapitalisation of WordPress does not count as a grammatical or spelling error (unless it’s in all lowercase at the beginning of a sentence, of course). Feel free to change it (I do), but only if you’re also doing something else.
I am not a frequent user of this site, and I have found that SE sites vary in several respects, including in their perception of the value of edits. On some sites, minor typo corrections are usually accepted with thanks; on other sites you can turn an ungrammatical unreadable mess into a useful question and still be rejected. This is partly the whim of the individual reviewer, but there are also cultural differences between sites. (Math SE doesn’t like edits at all, no matter how valuable.)
However, my edits on this site, including typo fixes, have usually been accepted. Yours should have been too.