Sounds like a pretty average reaction - the fact that he noticed, went to investigate without hesitation, and relaxed once he figured out the tractor bucket was nothing to worry about shows a pretty well balanced, clear-headed, dog.
Nervy/fearful would be freezing in place and refusing to move forward. Or running up to the bucket all hackles and teeth, barking his head fool off, growling at the bucket, lunging at it but never really getting too close, keeping up the defensive barking even though the bucket is completely inanimate (and by now, he should have figured out what the big object was, and relaxed).
So a good reaction for seeing something new in a completely unexpected setting.
A really strong nerved reaction would have been becoming alert, and casually trotting up to the bucket to check it out, or carrying on as normal, but occasionally looking at the bucket until he was close enough to recognize the object and then ignoring it.
But his reaction was not a bad one, probably pretty average.
PS: hope your dog liked swimming, otherwise might have been a challenge to clean him up from that last pic!