1. What does it mean?
이왜진 shortens 이게 왜 진짜, roughly 'why is this real?' It expresses surprise that an announcement, coincidence, product, or situation that sounds invented is apparently genuine.
Also written or said as iwaejin
2. The nuance
The phrase is a reaction, not verification. People can post it before checking a rumor, so seeing 이왜진 in replies does not establish that the underlying claim is true.
3. Examples
“농담인 줄 알았던 협업이 공식 발표됐어. 이왜진?”
The collaboration I thought was a joke was officially announced. How is this real?
“댓글에 이왜진이 많아도 원문은 직접 확인했어.”
Even though the comments were full of 'is this really real?', I checked the original myself.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.