If Spurs are interested in Matthews, it could explain why they say nothing about Splitter.
Matthews is a RFA but he has been with Jazz for one year. Jazz must use their MLE to match offers form other teams. However, Jazz have other needs and could use a part of the MLE on another player.
Spurs best interest in that case is to let Utah in the dark and not reveal what part of their MLE they will spend on Splitter. If Spurs had revealed how much Splitter would get, Utah would exactly know what part of their MLE they can spend to keep the ability to match an offer from Spurs. By keeping the Splitter transaction secret, Utah could move first to sign a FA with a part of their MLE and end up not being able to match an offer for Matthews from Spurs.