When they proposed it in South Tulsa they specifically said they didn't have a site plan in mind, it wasn't meant to imply it would be located here, they just thought putting it on the river "would be cool" for their presentation. The location was the playground and splash pad at ~76th and Riverside, from the apartments almost down to the volleyball courts.
https://www.youtube.com/watch?v=fIYB2AbVCGU (~4 minute mark)
That they did not move forward with the proposal to take 20 acres of park land and transfer it to a private entity (to include 10 acres of surface parking) is not surprising. The proposal basically called for several phases that ended with a new Expo like building (an "all weather" enclosed structure large enough for an indoor BMX track that could be reconfigured). That was a $45,000,000 plan made in August of 2015.
The expo square location is right next to their longtime home, Expo Center (or whatever we are calling it now), and the new facility is a $15mil investment (not $45mil). So I imagine it changed when they were advised $45mil and park land wasn't likely...