Are humans not sexual dimorphic? Can genetic XY but SRY not expressed become pregnant?
If you're asking if humans are a sexually dimorphic species, the answer is "yes".
If you're asking based on the viral response of the science teacher, then the answer is still, "yes".  What is described above are chromosomal abnormalities, or other disorders of development, but they are still describing sexual dimorphism in the phenotype. However, the answer itself is incomplete, as it's written out of political motivation.
Whilst true that a person can present, phenotypically, the opposite of their genetic sex, this isn't akin to them "being male/female" counter to their allosomes.  Of course, this in itself can prove to be a contentious issue - how is sex defined?  Under normal circumstances, phenotype is the obvious way of knowing. If someone has the external genitalia of a male, they can be assumed to be male, and vice-versa for females.  When it comes to chromosomal abnormalities, there is an "error" in devlopment, where the genotype is not properly expressed in the phenotype, and so while presenting as one sex, the "true" sex as determined by the genotype is the opposite.  It should also be noted that sexual characteristics can be ambiguous certain cases, creating abnormal sexual presentation, such as in hermaphroditism/pseudohermaphroditism, or "intersex" (the quote mentions 5-alpha-reductase deficiency, which is associated with male pseudohermaphroditism).

The problem with the quote above (at least in the way it is written) is it appears to suggest that chromosomes have little to do with phenotype, as in sex determination, and that this carries over to gender dysmorphic patients.  These are both mostly false.  Gender dysmorphic patients generally do not have any allosome abnormalities, and the reason that the given examples are deemed "errors" (eg XX male syndrome; 47,XXY) is because that is what they are, as well as being rare.  The typical effect of these problems is that the patient is infertile, (i.e. they are not sexually functioning, and have reduced biological fitness).

In short, the teacher is correct in the examples used, but overstating them with regard to the general population, and with regard to transphobia and gender dysphoria.  Humans are indeed sexually dimorphic but as with any complex biological system, errors expressing genotype can occur.