Unfortunately all disconnections and game crashes counts as leaving the match and will be penalized appropriately. The game server has no way to discern a legitimate disconnection or game crash from one that is forcefully caused by a dishonest player to bypass leaver penalties. You can learn about this policy here:
I am assuming this was a one time incident but if you have a history of disconnecting frequently, please avoid Competitive Play until you can resolve the issue. Remember if you see the message, “Lost Connection to the Server” in the title screen or the message “Failed to Connect to Server” in yellow text in the text chat box, this means there is something that disrupted your connection to the game server and not a problem with the game server itself. There can be a variety of reasons this happens including those that don’t disconnect your computer from the Internet. There is great troubleshooting to start with that can most likely resolve most issues and I encourage you to check them out here:
As always if nothing in that guide works, please reply saying you completed these steps and additional advice can be provided. Good luck!
(^^)v