That mass shooting took place about 1965 or so. There are documentaries made about it. There is at least one video on YouTube about it. A TV movie was even made about it. The times were different back then. Even the press was mostly credible.
You are completely right.
An important note, the young guys (mostly U of T students, possibly all students) went to their pickups and retrieved their .22 rimfire rifles from the gun racks. In 1966 this was not an uncommon thing at all in Texas, indeed even at UT.
They then proceeded to harass Whitman from behind cover with their .22s until the APD arrived. Two APD officers ran up the stairs and caught Whitman flat footed and shot him dead. My recollection of what I read about it is vague, but I seem to recall that Whitman not only had wounds consistent with the police weapons but he also had been hit by .22 fire.
I'm not sure about this either, but someone here posted that one civilian ran up the steps with the cops at the same time. That could have happened, but it would never happen these days.
It's a matter of opinion of course, but a salient point would be about the choice of caliber for a firearm in such a defensive situation. I think I'd opt for the .22 myself, yes the one in my truck (remember it's 1966 and not 2022, after all) rather than a deer rifle, lest I accidentally kill someone in the next county. Remember, all you gotta do is hit him bad enough to mess up his aim.