What counts as "getting away" for the cast master achievement in Animal Crossing New Horizons?

I can confirm from my own experience getting the first achievement, the following actions do not break your streak:

• Attempting to cast your line, but not being able to land in any water
• Casting your line in water without any fish nearby, and cancelling the cast
• Casting your line in water near a fish, and cancelling before it notices

However, as soon as a fish has spotted your dobber, cancelling it will break your streak. This is noticed easily by the fish disappearing.

Basically; if there is no fish, or the fish stays after cancelling, it was a 'safe' cast.

Just wanted to add for anyone checking this in the future, if you reel in before a fish has hit on your line, EVEN IF IT HAS NOTICED IT, it DOES NOT break your streak. I was at 54, cast poorly at a fish, and reeled in to try to reset. Before I hit A to reel in, the fish turned toward the bait and started approaching it, so when I reeled in, it disappeared. I found a different fish and caught it, and in a whim, checked my progress in the Nook phone, and sure enough, it jumped up to 55. I don't know if only losing fish that are actively on the line counts, but if they haven't even nibbled, you're in the clear.