If people are willing to believe they would inflate the number to seem more important, why wouldn't they believe that they would deflate the number to potentially save money on taxes? They weren't a public company at the time, so I could see internal financials being a little murky.
Does WWE really have a reputation of doing something like that at any point in their history? When 32's attendance came out as 80k, no one seemed to think they might be fudging the taxes even though the official pictures don't make it look like anything near 1/5 of the arena is empty. If the main crux of the argument is that the arena "looks" at or near capacity in official photos and camerework, then that is some pretty poor evidence considering it's pretty much the job of the guys taking those pics to make the attendance seem as impressive as possible. There's no way they'd make it easy to see the empty seats scattered around the top level.
32 came when the company was publicly traded and they weren't going to play games like that.
Wrestling has a long, long, LONG history that probably continues to this day of promoters claiming smaller houses than they actually drew when it came time to decide payroll or pay taxes.
Also, compare and contrast this (also professional) photo of the Hoosier Dome at WM8. You can do all the camera tricks in the world, there are clearly more empty seats in the upper balcony and on the floor than there are at Mania 3.
https://static01.nyt.com/images/2014/08/22/sports/Y-JP-MACUR/Y-JP-MACUR-master1050.jpg
Here's the 1994 World Cup also at the Silverdome, also with a pro photographer at virtually the same angle, also with visible swathes of empty seats.