A few aspects need review.
1. Giant Sequoia - For years, quite a few people spoke of widest Giant Sequoias in terms of girth at ground level where the trunk flare is most exaggerated. But professionals measure diameter and circumference near chest height known as dbh. So if you ever saw diameters listed for Giant Sequioa like 35 ft., that is exaggerated.
2. Coast Redwood - Historically, Coast Redwoods were wider and more massive than Giant Sequoia seen today. The volume was documented, but any Coast Redwoods more massive than General Sherman were cut down or fell in the early 1900s. Between 1930 and the present, Coast Redwoods are often described as the tallest redwoods and Giant Sequoias described as the largest redwoods. That left the impression that Coast Redwoods do not grow diameter comparable to Giant Sequoia. But between 2013 - 2015 a lot of new Coast Redwoods were discovered. These include trunk diameter and circumference at ground level that surpass all known Giant Sequoias. The world's widest trunk tree is a Coast Redwood with a diameter 29.2'
3. Baobab - Africa has Baobabs with very wide trunks. The largest are two or more trunks and do not contend for the world's widest trunk They are cool looking organisms though and if you haven't heard of them, search for some of the photos. Almost Disney-like.
4. The Montezuma Cypress, El Arbol del Thule - Regarding the Montezuma Cypress in Santa Maria de Tule, it has been described having a 46 ft. wide trunk. Here's the reality check ...
a. The trunk is very elliptical and does not look so big viewed from the narrow side, rarely shown. b. The trunk is very buttressed, inflating the dbh measurement. The tape literally floats in the air much of the way around. I included a diagram below to illustrate. c. El Arbol del Tule is most likely fused multiple trunks, evident from seams and included bark that show where individual stems grew and squeezed tight together over time. Over decades, air gaps between vanished as opposite bark grew together. d. Testing was done for DNA in the trunks leading to claims that proves its a single tree. But that is not proof, because trees can have the same DNA, then mature, expand and merge together. Both are possible, so DNA is not proof. This can happen from root sprouts, rooted cutting or layering. There are several ways it can happen. So the DNA testing is not proof. It only means the trunk is related to itself. And its clear from the appearance that it may be multiple trunks.