Oh wow, you're right lol. I think it's safe to say everyone understands the mechanism of spermatogenesis, but the definitions are confusing. After doing some more google image and Wikipedia searching, I believe you are correct.
I think it comes down to this: First Aid used the wrong nomenclature. By convention, N= the number of unique chromosome sets. And yes, the primary spermatocyte is called a tetrad, not a tetraploid.
Spermatogenesis should be like this:
Spermatogonia - diploid, 2N, 46 single chromosomes
Primary spermatocyte - diploid, 2N, 46 sister chromatids (tetrad/bivalent)
Secondary spermatocyte - haploid, N, 23 sister chromatids
Spermatid - haploid, N, 23 single chromatids
Sister chromatid = 2 identical chromatids. In the primary + secondary spermatocytes, there are still only 2 and 1 unique sets of chromosomes so they are still diploid (2N) and haploid (N). HOWEVER, the centromere has a pair of sister chromatids bound to it. Th extra copy is not a unique set, but rather just a duplication/copy of the original so it's not counted as change in ploidy. Ploidy only changes when you go from primary to secondary spermatocytes, since you actually are halving the # of unique chromosome sets. The # of unique chromosome sets does not change in any other steps.