César also apologised to Thai fans for failing to seal third place after losing 8-2 to the Uzbeks.
Thailand opened the scoring in the 2nd minute with a goal from Narongsak Wingwon, but Uzbekistan hit back with scores in the 3rd, 7th, 14th and 16th minutes to go 4-1 up at half-time.
Uzbekistan secured third place in the tournament with another four goals after the break while Worasak Srirangpairote grabbed a consolation strike in the 27th minute.
Japan were earlier crowned Asian futsal champions for the fourth time after beating Iran 3-2 in the final.
Coach César accepted the defeat, saying Thailand had done their best despite suffering injuries before the play-off against Uzbekistan.
"Last time we were eliminated during the championship's round of eight, but we entered the round of four this time," he said.