Support for the Rohingya cause across the region has a pop-up feel.
I looked up pop-up in Merriam Webster:
1: pop fly
2: a component or device that pops up
3: a pop-up book
4: a pop-up window on a computer screen
I guess pop-up feel has to do with the first definition, so does it mean the support of the Rohingya is very high, as a pop fly is? Or does it mean something else?
The writer of this article is probably a native speaker (or very good with English) but that doesn't mean the article itself is particularly well-written. For example, there is a paragraph where the word "seemingly" is used at least three times, when once would be more than enough.
"A pop-up feel" is not a very elegant turn of phrase. It's not a typical or standard English idiom, so we all have to guess what the writer means by reading the rest of the paragraph:
This North Caucasus bias was reflected in Yandex, Russia’s largest national search engine, reporting a sharp increase in searches about Myanmar coming from the region. Support for the Rohingya cause across the region has a pop-up feel. Many long-standing Islamic-themed Vkontakte pages have transformed themselves into 24/7 pro-Rohingya advocacy channels overnight.
It seems that "pop-up" means "appearing suddenly", or "without a long history". It would have been better if the writer had used the common English idiom "to pop up overnight".
Support for the Rohyngya cause across the region has popped up seemingly overnight.
I would guess that here pop-up means roughly the same as temporary, i.e. something that emerged quickly, but is unlikely to last long. The author of that sentence may be comparing the support for the Rohingya cause to other similar occasions. When the plight of some people once catches the imagination of the general population (may be due to some tragic event heavily reported in the news), but is equally quickly also forgotten.
Compare with pop-up restaurant.
The Merriam-Webster definitions don't seem to explain a relatively new meaning.
"Pop-up" is used as an adjective to describe anything which is organized in a manner which may be border-line illegal, and it only intended to last for a short time.
A typical example would be a "pop-up shop" that is set up in a building that is temporarily empty - some of these operate literally for only a single day before closing again, to avoid any legal action. Part of the customer attraction of the concept is in actually finding out about them (via social media, etc) before they close and disappear again.
Note, "pop-up shops" are now becoming a mainstream marketing technique, and organizations are renting out space for them, etc - the original "border-line illegal" implication is starting to die out.
A similar expression for one-off events that involve a crowd of people for a short time is "flash mob." That would seem a better description of some of the protests etc in the OP's link than "pop up".
I agree that the definition of pop-up is suddenly appearing, and this is probably what the author intends to convey. Wiktionary is a better resource for this word.
However, the full phrase is "pop-up feel". To say that the protests appeared quickly is a fact, not a feeling. I think that pop-up has a connotation of something artificially constructed. Pop-up implies that it is not a natural phenomenon, but instead has an underlying purpose. In politics, this is suspicious; it brings up associations like Potemkin village, astroturfing, and sockpuppetry. The author doesn't seem to intend this connotation because it isn't otherwise addressed in the article.
In Los Angeles and San Francisco, "pop-up restaurants" are a trendy thing. For short, they're just called "pop-ups." A pop-up is a location that is open only for a few nights and usually features a trendy chef serving a special menu. Finding out about these places is usually by word-of-mouth or Twitter. The pop-up locations, by nature, are makeshift; more attention is paid to the food than to the surroundings. Once the pop-up is gone, the space usually goes back to being to whatever it was before -- an empty storefront, a Halloween costume shop, what have you. The writer may have been referring to the fleeting, fly-by-night, chaotic nature of the support for Rohynga.
Amusing article: http://www.huffingtonpost.com/2015/04/10/pop-up-restaurants-study-people-more-obsessed_n_7035394.html
