Actually, calling an Amphisbaenian a lizard is like calling a legless lizard a snake, taxonomically speaking (and when we're talking about what to call a lizard, we're talking taxonomy). Even though people commonly only talk about lizards and snakes, there are three Orders of Squamates, and a lizard is to a snake as a snake is to an amphisbaenian, again, taxonomically. They're all suborders.

Now, the genetic closeness of "worm lizards" to actual lizards vs snakes is debated. One thing suggesting their closeness to the former is their reduced right lung. Snakes have a reduced or absent left lung (to better fit their noodley bodies - they just have one loooong lung). Idk about particular studies on this, but this looks like textbook convergent evolution to me. Of course, if the common ancestor of lizards and amphisbaenians came before that of amphisbaenians and snakes, it would just imply that maybe the lung differentiation was an even later evolution.

TL;DR: not a lizard, technically