This seems more like a personal style preference. At least for one line of code you could argue that it does not matter whether it's formatted as inline code or block code. Multiline code should definitely be formatted as a block.
We have a rejection reason that says:
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.
I would say the edit you mentioned falls under this category. If you are uncomfortable with it, just roll it back. But let me add that I would really encourage you to use block formatting instead of inline formatting. Inline formatting is supposed to be used for
code in a paragraph, whereas block code stands out as a separate paragraph. There's a semantic difference.
Since the post was done by a user with edit privileges, we actually can't review those actions until after they've happened. But that also means you have to trust the user to know what they're doing.
It's also not like they're trying to harass you. Trust me: if you're obsessed with nuances of formatting and proper punctuation, you'll find flaws everywhere. I'll probably go around editing single dash-hyphens (-) to en-dashes (–) for the rest of my life.
If you see a repeated pattern of such edits (i.e. when it happens to more than a handful of posts), it's worth investigating. Otherwise I would not care so much though. The user's edits I've seen are usually quite good (if maybe a little too much focused on minor details such as quotes and whitespace).