Does restarting Windows restart the SQL Server?
Assuming you have a single MS SQL Server instance on a single Windows machine the answer is a very definite resounding yes, restarting Windows will mean restarting all the services running on it including SQL Server.
If you had some sort of clustering with automatic fail-over etc. configured and your apps behave with it properly (i.e. they don't somehow bypass the mechanism and connect to single host), then like other multi-node solutions (load balanced web servers and such) you should be able to drain-stop the node and restart without it affecting anything else (other than a performance drop if you have an active-active load balances setup instead of mirroring with fail-over), then do the same on other hosts in the cluster to make sure everything is updated. Even with a fail-over or load balanced solution, when the updated node comes back into service there may be some impact as there will be nothing in the buffer pool so initial queries will be slower than usual until the normal working set is loaded.