What is "Sprinter" in the Netherlands?

Notice the icons on the Google Maps route.

Means a car route

Means a bus journey

Means a tram journey

Means a train journey

Slightly confusingly, the icons shown on the route are suggesting that this will be a bus journey, transferring to another bus. However, if you look in the directions pane on the left (on desktop, may be elsewhere on mobile) you will see the correct icons there. If you do not wish to be shown public transport options, then change along the tabs in directions from "any directions" (the arrow sign, which will show the fastest options in all modes) to the little icon of the car. Equally, if you only want public transport, there's a picture of a train. Cycling, walking and flight routes are also available.

It probably suggests the use of a train (sprinter) because the A1 is currently being constructed. There's a lot of traffic there usually and on some days it's closed down completely.

It is indeed a train stopping at all stations and speedy sprints between them. It is marked as an alternative because by car travel time is - much - longer in rush-hours on that particular route. When travelling week-days between 7:00 and 9:30 and 16:30 and 19:00 local time it is much faster,as much as 200%. Trade-off time and cost. It's like the M1 in England, that bad, to travel by car.