I think this is the real reason.
Another reason not to start Price in game 5 - so history won't repeat itself. In 2010 the Texas Rangers beat Tampa Bay in games 1 and 2 in Tampa Bay, Tampa Bay then came back to win games 4 and 5 in Arlington, Texas, however Texas won the 5th game in Tampa Bay. The starting pitcher in both Tampa Bay losses (games 1 and 5) was David Price - https://en.wikipedia.org/wiki/2010_American_League_Division_Series .
The 2010 ALDS sounds frighteningly similar to the current ALDS between Toronto and Texas, except with Toronto replacing Tampa. However, Gibbons broke the pattern by starting Stroman in Game 5 instead of David Price (perhaps Gibbons is much craftier than people give him credit for).
However, I think Gibbons craftily burnt David Price in game 4 so that there would be no possibility of him pitching long in game 5.