The compound shown is 1-ethyl-2-methylcyclobutane with no configuration specified. Treating the ring as planar and considering configurational stereoisomers only, which statements are correct?

C1 (bearing ethyl) and C2 (bearing methyl) are stereocentres with different substituents, so the mirror plane that makes cis-1,2-dimethylcyclobutane meso does not exist here. Both the cis and the trans isomers are chiral, giving two pairs of enantiomers and $2^2=4$ stereoisomers in total. cis and trans differ at only one centre and are not mirror images, so they are diastereomers.