Supposed low temperature of calcium carbide synthesis
Liu et al. in 2012 [1] showed experimental data that lead me to believe this to be inaccurate. Two relevant informations from their findings:

$\ce{SiO2}$ and $\ce{Al2O3}$ do not react with coke at temperatures lower than $\pu{1460 °C}$, but they do react with $\ce{CaO}$ to form $\ce{Ca3SiO5}$ and $\ce{Ca2Al2O5}$, respectively […]
Note that the behaviors of $\ce{SiO2}$ and $\ce{Al2O3}$ observed in this work do not agree with some literature, which reported that both $\ce{SiO2}$ and  $\ce{Al2O3}$ reacted with coke at temperatures of $\pu{∼ 1200 °C}$.

Also, in Fundamentals of Metallurgical Processes: International Series on Materials Science and Technology [2, p. 174] it is written that calcium carbide is not stable in the presence of silicon and undergoes the reaction:

$$\ce{2 SiO2 + 2 C + CaC2 &lt;=&gt; Ca + 2 Si + 4 CO}$$

References

Li, G.; Liu, Q.; Liu, Z. $\ce{CaC2}$ Production from Pulverized Coke and $\ce{CaO}$ at Low Temperatures—Reaction Mechanisms. Ind. Eng. Chem. Res. 2012, 51 (33), 10742–10747. DOI: 10.1021/ie300671w.
Coudurier, L.; Hopkins, D. W.; Wilkomirsky, I. Fundamentals of Metallurgical Processes, 2nd ed.; Hopkins, D. W., Ed.; International series on materials science and technology; Pergamon Press: Oxford [Oxfordshire]; New York, 1985; Vol. 27. ISBN: 978-0-08-032536-1, eBook ISBN: 9781483162409, DOI: 10.1016/C2013-0-03773-5.