I'm not an Indonesian, but I did live in Indonesia for 2 years. From what I understand, it was a phrase being spammed all over the social media profiles of famous DJs, so they decided to make it famous by including it in some of their music. I'm still confused, as well, why it suddenly caught on like wildfire. After living there and seeing people on the side of the road shouting 'Om Telolet Om', I can't see why it's special, except that Indonesian buses like to customize their horns to have really distinct sounds. I guess maybe people thought the customized horn sounds would work well in DJ remixes and such?

The article posted by Yuri helped me understand a little bit better why this is happening.

Here's also an example of a DJ group, Firebeatz, showing their social media comment spam and the music they responded with:

https://www.youtube.com/watch?v=tPmz6iuOZlo

I lived in Indonesia for about two years; 5 months in Malang, 5 months in Bekasi, 4 months in Bogor, and 7 months in Solo. I really loved living in Bogor and Solo. Waktu itu saya juga sering ke Jakarta. Selain itu, saya pernah ke Surabaya, Magelang, Yogya, Cisarua, Boyolali, Batu, dan beberapa kota lain. Setiap kota punya keindahan sendiri. Indonesia is so beautiful!