There is, as yet, no word on what specifically the disagreement was about, but apparently Lesnar was furious by the time he reached Gorilla Position. He proceeded to express that fury toward Vince, who himself became angry in turn.
The exchange ended with Lesnar throwing the Universal Title belt, either at Vince or at the wall (details are spotty), and stomping off. The Sheet says there is a belief Lesnar may have gone off-script toward the end of his match with Roman Reigns but that cannot be confirmed at this time.
Dave Meltzer on Wrestling Observer Radio said that Shane McMahon was actually with his father when the altercation went down. After the belt was thrown, Shane is said to have jumped up to get involved and was posturing for a scrap with Lesnar. They had words but eventually Lesnar took his leave with Paul Heyman in tow.
Apparently Reigns was expected to win the ‘Mania main event and the decision to have him lose was made very last minute and kept secret. Even the ref supposedly didn’t know the finish until the match was already underway. The extent to which the finish of the match was worked backstage has led some to speculate that even the backstage altercation afterwards could also be a work. However, those present at the time felt it to be a shoot.
It was announced the day after ‘Mania that Lesnar has re-signed with WWE, but PWInsider reports that the deal is not a long one and may just be an extension of the old one. Lesnar is scheduled to defend his title against Reigns in cage match April 27th in Saudi Arabia at the Greatest Royal Rumble event.