Figured it was LaTeX, but wanted to make sure. So, there are 2 possible fixes for this.
The first is to define quotes properly. That is, using " renders incorrectly. I'll be honest, I didn't know about that until I came across the following post (link). I think this would be the correct thing to do.
The second method is to modify the tmLanguage file. The following scope is being applied to that string invalid.illegal.string.quoted.double.latex. You can remove the associated pattern from the tmLanguage file, and it should stop that highlight from occurring. If you want to take this route, let me know and I can provide some additional instructions on how to do it.