“No doubt” is probably a bit too strong at the moment, until Malaysia Airlines and/or Boeing engineers have looked it over and reported their results, but the odds this came from MH370 are rather high.
Shouldn’t take long for confirmation. They don’t even need serial numbers(which are probably on there). Just a conclusive ID as a 777 part, MH370 is the only 777 it could possibly have come from.
This solving the case is a longshot, though. Small chance they’ll be able to determine if it was an in flight breakup or a breakup on impact, but that’s likely as far as they’ll get with what they’ve found. What may be more important than this specific part will be using the fact that it turned up here to plan out further searches for more debris, which might give them enough to crack the case.