It’s a DHT derivative, but it does have a progestagenic effect.
From Anabolics 11th Edition:
It is important to note that oxymetholone does not
directly convert to estrogen in the body. This steroid is a
derivative of dihydrotestosterone, and as such cannot be
aromatized. Anti-aromatase compounds such as Cytadren
and Arimidex® will, likewise, not effect the relative
estrogenicity of this steroid. Some have suggested that
the high level of estrogenic activity in oxymetholone is
actually due to the drug acting as a progestin, similar to
nandrolone. The side effects of both estrogens and
progestins can be very similar, which might have made
this explanation a plausible one. There was a medical
study examining the progestational activity of
oxymetholone, however, and it determined that there was
no such activity present.3 With such findings, it seems
most plausible that oxymetholone can activate the
estrogen receptor, similar to, but more profoundly than,
the estrogenic androgen methandriol.