By all means, if New Zealand is worried about Fiji military coups, then it's the duty of New Zealand's intelligence service to monitor the Fiji military.
The problem isn't that some nation is spying on some other nation, it's a problem of scale and scope. Fearing a military coup does not warrant "intercepting and storing content and metadata of all communications" happening on that island.
The problem isn't that some nation is spying on some other nation, it's a problem of scale and scope. Fearing a military coup does not warrant "intercepting and storing content and metadata of all communications" happening on that island.