I am trying to avoid construction traffic on Friday morning drive and found a route marked "Sprinter". What does sprinter mean / imply in the Netherlands? Is it a bus? Is it not for driving?
'Sprinter' is the name for the train service that stops at each station.
The alternative are the 'Intercity' services that only stop at limited stations.
The route you have selected first uses the sprinter train from Schiphol Airport station to Naarden Bussum station, there you change onto bus line 101 which will drop you off at the AmersfoortseStraatweg in Naarden. That is why, as Willeke commented, you (also) see the bus icons and the route following the roads (the small final leg):
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 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.