Updating tvOS does not update the screensavers, it will use the ones already downloaded, new ones are downloaded on the cycle you select here:
Settings>General>Screen Saver>Download New Video>
selections are:
Never
Daily
Weekly (default)
Monthly
Depending on your setting here is when you will get new screensavers.
Doing a reset just deletes the screensavers already downloaded so it has to download new ones upon startup. You could switch it to Daily, then you'll have new ones tomorrow.
But, if you're impatient, go ahead and reset your ATV just so you can have new screen savers now.