Okay - I think I've figured it out. Click/swipe doesn't work on all the buttons or all the time (don't know why), but here's what you do:
Click on the start cell. If it doesn't turn green, try swiping. If that doesn't work, click again.
If it turns green, swipe in the direction you want to fill in. Those cells should turn green. Sometimes the original cell turns grey again; if this happens, start over.
If your target cells are green, you have to go back to your original cell and click once (without swiping). The green cells should fill in.
Sometimes you click/swipe and a cell becomes green, and then you can't do anything. Sometimes you click/swipe and the cells fill in. Haven't figured out any pattern. Just doesn't seem to reliably work.
There's just a title screen. Clicking on the words "Rusty Lake" takes you to their website. Clicking on anything else (including the three dots) does nothing.
Simple game, but achievements did not register. Since it says you have to go to the main menu to register them, I don't even have a screenshot to send in. Oh, well. Wasted some time.
I am aware of this issue, sometimes unity doesn't properly detect when a drag event has ended, this has been fixed.