everybody will choose to bet real sociedad as they are in better situation than deportivo la coruna even they play at home , the result just surprising.
You kinda seems to confuse yourself in the last part of your post, it should be choosing deportivo rather than real sociedad instead. If you watch through the match you can see how deportivo was dominating the game and with just some luck they managed to turn all that attempts into goals and won the game
so i clearly bet for real sociedad to get at least a draw as they are in better situation (in 4th place of league table) where deportivo struggling to avoid relegated.