How can a drone be male?
The short answer, which has already been pointed out by user137, is that females are diploid while males are haploid. Bees do not have sex chromosomes per se; rather sex is determined by the csd gene on chromosome III (csd stands for complementary sex determination). Diploid bees that are heterozygous at the csd locus (i.e. contain two different alleles (versions of a gene) for csd) are female (workers).

Bees that are haploid at the csd are males. Interestingly, diploid bees that are homozygous at the csd (i.e. contain two copies of the same csd allele) are also males. But in the honey bee, these bees do not survive as they are killed by workers before they mature. In some other haplodiploid species, however, both haploid and diploid males are viable (the bumble bee Bombus terrestris for example). Also note that diploid honey bee drones can be viable if they (somehow) make it to maturity without being killed by workers (e.g. see here).