Typo in Morton Knots notes?

Question

apologies if I'm just missing something obvious. I'm reading the H.R.Morton "Knots and Links" notes with no background, just for fun, and I'm in section 2, where two great circles have been defined (p.11): $$ C_1 = \{ ((x_1, x_2, x_3),t) \in S^3 : x_1 = x_2 = 0 \} $$ and $$C_2 = \{( x_1, x_2, x_3), t) \in S^3 : x_3 = t = 0 \}. $$ Later, we switch from thinking of $(x_1, x_2, x_3, t) \in \mathbb{R}^4 $ to $(z_1, z_2) \in \mathbb{C}^2$ with $z_1 = x_1 + i x_2$ and $z_2 = x_3 + i t$ (bottom of page). Then I see why $S^3$ is given by $|z_1|^2 + |z_2|^2 = 1$, but then they say $C_1$ is given by $z_2 = 0$ and $C_2$ is given by $z_1 = 0$. This continues throughout more discussion in examples, the idea that $C_2$ is associated with $z_1 = 0$. But I just thought that it should be reversed, $C_1$ given by $z_1 = 0$ because $x_1 = x_2 = 0$ in there, etc. Am I just going crazy?