${\mathrm{Be}}_2\mathrm{C}\text{ and }{\mathrm{Al}}_4{\mathrm{C}}_3$ are called — 

Because they react with water to form methane gas  

$\underset{\mathrm{Aluminium} \mathrm{carbide} }{{\mathrm{Al}}_4{\mathrm{C}}_3+ 12{\mathrm{H}}_2\mathrm{O}}\underset{ }{\to } \underset{ \mathrm{Methane} }{\mathrm{Al}{\left(\mathrm{OH}\right)}_3+ 3{\mathrm{CH}}_4 }$
${\underset{\mathrm{Berylium} \mathrm{carbide}}{{\mathrm{Be}}_2\mathrm{C}}+4{\mathrm{H}}_2\mathrm{O}}_{ }⟶2\mathrm{Be}(\mathrm{OH}{)}_2+\underset{\mathrm{Methane}}{{\mathrm{CH}}_4}$