Mountain and forest in Indonesia is not same as in Europe. I will not say one is more difficult or easier to handle, than other, but it’s just different. The condition might also change quickly.
Some people is over confidence or under estimate and many case do not have enough knowledge to handle different situation.
Having local guide would help to avoid some trouble. I will not judge their quality as I’m not competent. I prefer to simply to using subjective term - bad and good guide. To my experience, many of them are quite good, have lot of experience and very familiar with local condition.
No need to wave with 100 Euro bill, I’m sure they will help you if you get into trouble. I don’t think the guide(s) and local villager probably who found and help this german tourist were asking for money.
When I was student in Jogja, I climbed Merapi dozens time and often alone. Years later, I came back again to Yogya and with high confidence climbed Merapi without guide. I was lost and trapped in a situation where was difficult and dangerous to move forward or return. Luckily, after more than 2 hours struggling on a cliff, a local guide found me and help to get back.
Since then I really appreciate the local guides, not always use them but at least I will listen their advice.
For scuba diving in Indonesia, I love to use local guide, most of them are good or very good guide although their certification/training level is below than mine. In location like Lembeh as a example, a local dive guide with only certified for open water could be much better than expat dive instructor.