Yeah,you're right. the pinyin of 茅台 is "Máotái",not Moutai.According to the web,"MOUTAI' is the international registered design,not pinyin.Foreigners read "茅台" like that originally,People consider that this pronunciation has a high reputation,so they name 茅台 as this way which isn't pinin.
据称,“MOUTAI”是茅台酒的国际注册商标,并非汉语拼音。最初外国人读“茅台”二字就这样发音,考虑到此读音在国际上已具知名度,公司干脆就给茅台酒取了这个音译名。