The games that aired in 4K last season were the home games specifically. Rogers only has 4K recording and broadcast facilities in Toronto. The content on Sportsnet is controlled by Rogers so if they broadcast in 4K, assuming no technical issues, it should be available in 4K.
The game tonight vs the Yankees is listed on Sportsnet's website as appearing to be in 4k. >> https://www.sportsnet.ca/schedule/
Only thing I can think of is either the guide is using a generic description for the game from another Sportsnet channel and it will be in 4K, or Rogers/Sportsnet may not be broadcasting the game in 4K due to some possible technical issue.