Was this a theme song to the television show? "There's a man you've seen on the television screen" seems like an odd line for a song introducing the show itself.
By the way, I too was a big fan of Hopalong Cassidy and his ten-gallon hat. The show came on right at the end of my nap-time in the mid-1950s. Four o'clock, I think?
By the mid-sixties I prided myself on knowing all the cowboy show theme songs by heart. There were tons of them, too. You're making me wonder, now, if I left one out.