I wouldn't call it disregarding grammar.
In this case I think that both titles are correct. The first one refers to a hydrogen [atom], while in the latter it refers to hydrogen in general. As such I support the decision to reject it, as it does not significantly improve the state of the question. The reason given by the reviewers reflect that:
This edit does not make the post even a little bit easier to read, easier to find, more accurate or more accessible. Changes are either completely superfluous or actively harm readability.
Edits bump the question to the top of the active tab of the homepage. As such they should be a substantial improvement over the current state. Removing an article (which I think may or may not be there) does not achieve that.