Sorry, I have questions/comments…
I wonder if Smith was a made up surname.

Was your great grandmother headed back to Ireland c1931 (if you don’t mind sharing)?
Regarding changing occupations…some of my ancestors had very different occupations after they arrived in Canada, I wouldn’t be too concerned about a possible occupation change for Malcolm if he sailed to/returned to England.
1931 Toronto Directory
Malcolm emp Eatons. h 2 Chudleigh [Eatons - department store]
Malcolm D (Smith Bros). h 15 Bellefair av
Malcolm F emp CNR r 73 Osler [CNR - Canadian National Railway]
Note: I removed the link that I originally provided here. I’ve used the site in the past with no problem. However, my iPad has been extremely sluggish since opening the site a few minutes ago and I don’t want anyone to experience the same problem.
Added: 1932 directory
Malcolm was a salesman at Eatons
Smith Bros. were bookbinders