A 35-year-old man from Delhi presents with palpitations, tremor, and heat intolerance for 2 months. Examination reveals a diffuse, tender thyroid enlargement with a bruit on auscultation. TSH is <0.01 mIU/L (normal: 0.4–4.0), free T4 is 28 pg/dL (normal: 8–18), and free T3 is 9.2 pg/mL (normal: 2.3–4.2). Thyroid peroxidase (TPO) antibodies are negative. Radioactive iodine uptake (RAIU) is elevated at 65% (normal: 10–30%). Which of the following BEST explains the suppressed TSH in the presence of elevated thyroid hormones?