This is indeed perspective distortion from wide angle lenses (like your selfie cam):
The influencer-type “holding up a phone in the mirror” shot is actually technically sound, because it uses the phone’s longer-focal-length camera.
And typically this is the camera with the biggest sensor.
(I realize this is just a meme, but I can’t help spreading photography bits like I’m crazy).
In practice, people use the term “focal length” as field of view/zoom for the final image, especially when we start talking smartphones and full-frame “equivalent” focal lengths.
I don’t disagree, the article I got this image from explains exactly what you did, but… I think the semantic ambiguity is acceptable, in this case. The actual angular field of view in a shot isn’t advertised in specifications. Neither is the sensor crop factor in post processing. It’s all kind of impractical to calculate, so using FF equivalent focal length as a “zoominess” standard people can understand makes sense.