Translation:That teacher is not fat.
胖Pang4 could be a positive word for older generation where Pang is a sign of having enough food and nutrition . This has to do with the lack of resource as a country in the old days where people are generally very lean in a normal household. This is especially true in the emperio ages. So 胖 is often used to wish the infrant or kids to grow healthy and live well. Phrase like 白白胖胖。 In fact, "肥” should be the direct translation of “fat” which is socially negative most of the time.