The evidence seems quite good that this was intentional. The paper found evidence of both using stone tools and fire to shape the notches. Using fire as an aide

The evidence seems quite good that this was intentional. The paper found evidence of both using stone tools and fire to shape the notches. Using fire as an aide to woodworking is well known and still exists today in some traditional forms of woodworking. I don't see anywhere in the paper saying the entire structure was burned, just the faces of the notches. They were able to reproduce the chop marks they found with recreated stone tools of the time. Given we know stone tools were used for more than 2.5 million years by the genus homo, I don't see why it's a stretch to say they were using stone tools on wood 2 million years into having stone tools. Lack of evidence does not mean lack of occurrence. It is very difficult to find organic matter from so long ago given that it normally decays. Furthermore, this is not a radically complex structure either. Something a child could make. > We interpret the notch as intentional, made by scraping and adzing1 to create a join between the log and trunk, forming a construction of two connected parts. Infrared spectroscopy (Supplementary Information Section 5) provides indeterminate evidence for use of fire in shaping the notch. Clark17 described a similar find, from the Acheulean in Site B, of comparable length (165 cm long) with a “wide and deepish groove” transverse to the long axis, with tapered ends. He interpreted the groove as anthropogenic and suggested it was part of a structure. The excavation of two interlocking logs in BLB5, with shaped ends on both objects supports this interpretation. We know of no comparable construction in the early archaeological record. https://www.nature.com/articles/s41586-023-06557-9 https://www.nature.com/articles/s41586-023-06557-9