I can't find a way to disable autoplay from Google Classroom posted videos. If you embed the video, you can restrict autoplaying to the same channel as the original video by adding rel=0 to the video embed.
Testing:
https://swccd.instructure.com/courses/7697/pages/get-rid-of-the-suggested-videos-in-an-embedded-youtube-video
https://developers.google.com/youtube/player_parameters#release_notes_08_23_2018 states that rel=0 restricts the suggested videos to the same channel that posted the original video.
Link with rel=0:
https://youtu.be/LyC855KdBKo?rel=0
Link without rel=0:
https://youtu.be/LyC855KdBKo
With rel=0:
Without rel=0: (default)
Link with rel=0:
https://youtu.be/vpH9r1RIhPE?rel=0
Link without rel=0:
https://youtu.be/vpH9r1RIhPE
With rel=0: This one worked!
Without rel=0: (default)
