Express Hello World -- Heroku Foreman Returns Code 5, 'npm start' works just fine

I'm following a tutorial in which I created a simple "Hello World" in Express. The tutorial gets everything up and running locally just fine with 'npm start'. The tutorial then moves on to prepare for uploading code to Heroku via Toolbelt. Following the directions (so far as I can tell), I execute 'foreman start'. When I hit the localhost URI, I get the basic HTML I'm expecting, but no CSS (no doubt related to the ERR_CONNECTION_REFUSED outputs I see in the console window, which is probably related to the whole server being shut down). Looking at the output from the command line, there is the text:

exited with code 5
sending SIGKILL to all processes

I've searched Google for what Foreman's code 5 is, but didn't see anywhere that discussed code 5. I downloaded the source code for Foreman on http://ift.tt/L5wPH5, but still couldn't figure out what code 5 is (!?!?). I suspect I could work out the issue if I knew what code 5 meant. Anyone out there know what it is?