Bengtsson, who placed fifth in the contest, said Sobral's speech was "below the level of a true winner".
Receiving the award on Saturday for his understated, jazzy love song Amar Pelos Dois, Sobral said: "We live in a world of disposable music; fast food music without any content. I think this could be a victory for music with people who make music that actually means something.
“Music is not fireworks; music is feeling," the 27-year-old told the audience in Kiev. "So let’s try to change this and bring music back.”
But Bengtsson, who performed his synth-pop song I Can't Go On while walking on an electric treadmill, has hit back at the crooner's comments, defending "fast food" music.
"Congrats on your victory, I really like your song and the way you sing it, but I think your speech after winning the ESC was below the level of a true winner," Bengtsson wrote on Instagram. "'Fast food' pop music can be the best thing in the world at the right place and time, so can a song beautiful as yours."
Sobral was the first Portuguese entry ever to win the annual contest; Sweden, by contrast, has won six times. Sobral's winning song was written by his sister, singer-songwriter Luísa, who joined him onstage for his encore performance.
Neither the Sobrals nor Bengtsson are strangers to the "fast food" music world; all three singers have previously competed on their national versions of Pop Idol.