Pusaka, what museum was this supposed to have been in? Did this information come from the museum itself or the guy trying to sell the spear? Two points i'd like to drive home here:
1. Sellers have been known to lie inorder to get high prices for low value items.
2. Yes, museums, even good museums can and have been wrong about all kinds of things that have been in their collections for years. This is especially easy in the field of ethnographic edged weapons and
especially especially easy when it comes to weapons of Indonesia. The fact is that there are very, very,
very few people who can be considered "experts" on these weapons, even in Indonesia itself where the larger part of the population have, for better or worse, but this aspect of their heritage behind themselves. So even if the seller wasn't tell you a fish story this doesn't mean that the museum didn't have it completely wrong. If i were you i would consider youself luck you were late getting to this auction.