This one is tricky.
There are definitely some (strong) signs that the question should be on topic:
It's clearly interesting to historians and history buffs
The upvotes on the question and on your answer, and the lack of close votes are proof of that.
It was answered, correctly and fast
Correctly obviously being the important part, fast the "nice to have" part.
But, there are also problems:
It's a non searchable question
The title is awfully generic, and I don't think there's much room for improvement. The question text is... what question text? All we really have to go on in terms of searchability and categorization is the tags. And those are awfully generic as well.
This is an important issue, as this type of question is practically undiscoverable through search engines, and thus not particularly useful in terms of helping the site grow. That of course is no reason to outright ban the category, but it certainly reason enough for me to not be particularly enthusiastic about further encouraging similar questions.
A related issue is that the type is also not particularly accessible, as is typical with media heavy content. While I realize that might not be a very important factor for most, it is for me.
It's sort of a guessing game question
Almost every Stack Exchange site has it's own "guessing game" questions, and they've proven to be more trouble than they are worth. This type of question shares a lot of characteristics with "guessing game" questions, although I don't think it fits the description 100%.
We are of course free to decide on our own what kind of questions we welcome on the site (within certain broad limits) and I'm not saying that we should outright ban the category just because similar categories didn't work elsewhere. But, it wouldn't hurt to take notice of the experience of others and not repeat the same mistake.
The low end of the quality spectrum is going to be awful
Ok, this is more speculation than fact. But I'm afraid that while the question in question is good, the low end of the category is going to be truly awful. Stuff like either extremely well known pictures (that will bore most of us very quickly) or extremely low quality pictures, from weird angles, etc.
And, just to push my paranoia up to eleven, the category offers a lot of opportunities for trolling. I have quite a few pictures that look like they are somehow historically significant but aren't really (just old), and I can troll the site's crowd right now by having you all going around and trying to answer unanswerable questions.
I'll stop here, because this seems to be turning out a lot more gloomy than I originally intended. My take is that I don't see any reason to outright ban the category of questions but at the same time I don't see any reason to encourage them as well. If they continue appearing, so be it, and we'll deal with any problems as (if?) they appear. If not, meh.