I did something similar almost one year ago but never shared it. From the video you posted I imagine he is following the same principle as I did, which in summary is:
- Get room boundaries and apply an offset inwards.
- Create analysis points (eaither as a grid on the room, its corners, doors, etc.)
- Create lines from the origin to each point and removing those no valid (intersecting boundaries or other criteria).
- Using Curves.ShortestWalk node from Lunchbox package to find the shortest distance.
- Represent the path. I used analysis points as is quite visual, but other options would be to create detail lines or 2-point adaptive families so they can be tagged/scheduled.
I’ve just uploaded a video on youtube with a demo I did on January: Shortest Path Computation In Revit using Dynamo.
I was driven to develop this after reading same post @awilliams refers to. After I made it work, this other post was published with a similar method. As I did it one year ago, now I realize there are a few (lot) things that can be heavily improved, so that´s the reason I don´t want to share the file just yet. Hopefully the logic described plus all the resources on the posts are enough to start