I don't have actual info on Manobo's instrument, but if you look at the design I wouldn't say it's farfetch.
Here's the bamboo zither elsewhere in insular SEAsia. Unlike the Filipino version, theirs (Bornean tube zither) is bigger and uses two sticks.
Here's a sesando from Timor, it also uses wooden concave to channel the sounds.
HOWEVER, this particular 'instrument' was supposedly created so....:
"Caleb had a dream in which he gave an unique musical instrument to the Tinananon Manobos. The dream was so clear that Caleb was able in three months to build that instrument. In a back of a jeepney carrying pastors to a meeting, one man kept staring at Caleb, trying to remember when he had seen him before. Then he realized he had seen Caleb in a dream 3 years earlier...& this missionary worked with him. Last month, together they took that
instrument to a Tinananon Chief—who was stunned by it. He took Caleb into the music room where there was an empty spot for their Salimbaa this instrument they’d lost 100 years ago."
[url] http://gp-email.brtapp.com/files/gpconnect/11.19.14/int_11.19.14_newsletterlinks_davidupp_updated.pdf [/url]
-roflmao2
But it's possible he researched it or heard about it and did a close reconstruction (or the actual person that build it was that 'native missionary' who actually conceptualized most of it) then saying he heard God tell him so...but so far I'm hearing = -lmao White people's God complex.