Here are the games and stats that Sean played in this season for Bradley-
https://www.espn.com/mens-college-basketball/player/gamelog/_/id/4592676/sean-houpt
Note that the first 6 games he appeared in were non-conference games that were pretty much all major blowouts.
The next 5 games he played in were conference regular season games that he got minutes because of the injuries & illness to Elijah Childs, Darrell Brown, and Ville Tahvanainen. And he got a few seconds of playing time in the Championship MVC Tournament game against Valparaiso when Darrell Brown was removed to get a well-deserved ovation from fans.
His scoring high (8 points) was the Feb. 1 game at Loyola when he made a couple threes. His high minutes (15 minutes/0 points) came in the Jan. 25 game at Indiana State when Bradley was missing Childs, Brown, and Tahvanainen, Nate Kennell was in foul trouble, and Bradley had only 1 other available bench player (Ari Boya). So Sean's presence in that game was a necessity, though Bradley lost the game 61-53.
He was a valuable practice player and a well-liked teammate. But he probably wants more chance at playing time in his remaining college career. I can't blame him for taking the step of entering the transfer portal.
Btw, if he has indeed entered his name into the NCAA Transfer Portal, this doesn't necessarily mean he will transfer. Entering the transfer portal allows him to make contacts and look for other options without violating NCAA rules regarding tampering. But he could still decide to return to Bradley (Javon Freeman-Liberty did that last year). Since Sean is not a scholarship player, there is no concern about losing his scholarship to another recruit.
So far, there has not been any report about Bradley's other walk-on Riley Burger, who never played this season because of an injury. There is a possibility he could return to the team next season. If he regains his health, he might be able to provide what Sean was able to give the team this season.