While their language is mild and friendly, their message is utterly patronising.
To me, that is not patronizing. Just like your original comment about the photos and the original reply, this is all subjective.
That you chose to take offense to subjective, measured comments is something you may want to spend time considering.
> you could go find better examples (with a free license) or take your own and add them to the article.
That
> they decide to explain to me that I can edit Wikipedia!
is simply untrue. Had that been the case, I’m sure everyone would agree it was patronising.
However it does not say "you can edit Wikipedia," more like "if you think there is a problem, you are free to fix the problem."
Indeed English can be ambiguous, but I do not think that can be interpreted as patronizing.