The description below the Sneak 100 achievement is unlike the others. Most of the other achievements give a command/order to the user, telling them what to do, for example:

"Create and fully power a Beacon," or

"Collect dragons breath in a glass bottle."

However, Sneak 100's description has a gerund (-ing) at the start:

"Sneaking next to a sculk sensor without triggering it."

Just a parallelism issue.