Would we expect them not to? "An important developed nation is picking a new fighter. Let's know nothing until it's over with." is hardly good stewardship of your own nation's trust and resources. It's the NSA's job to monitor who is friends with whom so policy makers can make policy. That's not to say the NSA should do anything they can. But it is their proper job to spy on non-Americans for America.
The problem isn't the spying, it's their duty after all. The problem is the suspected strong arming that may or may not have occurred behind the scenes. I remember a Dutch politician that was vehemently opposed to the F35 that died in mysterious circumstances. I would normally put this on coincidences but when the stakes are that high I won't go for Ockham razor first.
It seems like a huge overreaction to murder a single vocally opposed politician just over a aircraft fighter deal - even if he was a critical decision maker (which I'm going to guess he wasn't).