RENTON, Wash. — When Seahawks receiver DK Metcalf returned last week to Seattle from Germany, he was almost $30,000 lighter than when he left. But exactly what Metcalf did to earn a hefty fine from the NFL for a personal foul he received during Seattle’s 21-16 loss to Tampa Bay in Munich will remain a mystery. Metcalf was penalized after arguing with side judge Allen Baynes that he had been interfered with by Tampa Bay cornerback Jamel Dean on a fade route in the end zone on a third-down play in the third quarter with the Seahawks trailing 14-0. Baynes threw the flag as Metcalf left the field,…