Other mistake: After rescuing the boy and his dog from the structure fire, when both of 51's rigs are backing up the driveway, the office door opens and we can see through the glass door that someone is standing there, even though they're all on the rigs. Next shot, that phantom individual has vanished.
Other mistake: When Station 51 is dispatched to the structure fire in the middle of the night, once they arrive at the burning house, one of the first shots shows a crowd of bystanders, many in their robes. That footage is from season 1, the pilot episode "The Wedsworth-Townsend Act", during the factory fire at the start of that episode.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.