There's a difference between "I don't want to set my expectations too high" and "Will the White Sox beat the Astros? Probably not".
You are fully correct the White Sox would be underdogs in that series, having lost the season series to the Astros 5-2 and assuming the Astros hold onto the #2 seed. I can see lots of ways that goes badly for the White Sox and would really like to pass the Astros for that #2 seed, but I won't get anywhere close to "The White Sox probably will lose that series".