I suspect a high percentage of their athletic giving is done by non-alumni.
As noted in the article, in the old days the state provided almost all of the funding for all of the state schools, LSU and Tech included. Probably all of the state schools have lower endowment than comparative schools in their respective conferences for that reason. Tech has had some endowment for a long time. I had a Tech Foundation Scholarship my freshman year (1965-66) equal to about 1/3 of the total cost of attendance. Mainly that was what the endowment was for with the state paying salaries and other operating/maintenance/capital expenses. The "registration fee" was only $50 per semester with a few other student fees added on which brought cost of registration to about $65 per semester. There was no tuition per se. Actually when I went to UH back in the early 80s tuition was only $4/hr which came to about the same amount.
To be sure, the appeal of LSU sports extends far beyond the university's alumni. Rick Perry, president of the Tiger Athletic Foundation, said 40 percent of the group's donors did not attend LSU
2015 LTAC Champion donor (110%)
2015 Football Season ticket holder X2
43 million is way more than I thought it would be.