"Jesus washed only His disciples feet at the first Holy Thursday.  Francis washes the feet of disciples and non-disciples when commemorating Holy Thursday."

It's been my understanding that only disciples were present at the Last Supper.  We don't know what our Lord would have done had there been non-disciples present.  And, arguably, by washing the feet of Judas, who Jesus knew had betrayed Him, I would say He extends the sign of foot washing beyond the boundaries of his loyal followers.