A better title is "How is a portable medium wave or longwave radio receiver possible?"
The FCC now allows for AM medium wave broadcast stations to convert to digital (HD) only. This causes many engineers to cringe at stations using branding such as "Digital AM"[1] or "AM HD" since there's no AM involved.
Even the FCC calls it "All-Digital AM Broadcasting"[2].
[1] https://www.am1230digital.com/ [2] https://docs.fcc.gov/public/attachments/FCC-20-154A1.pdf
For a domestic radio, AM / FM just means low / high fidelity, and users just see two sets of numbers 520 to 1602, and 88 to 108 (in the UK). I doubt most people belly feel the physics of it, or that the latter is higher frequency than the former.