During my uni days I had a math lecturer who stated that it was a matter of great pride to him that all the math he created was pure and had absolutely no pract

During my uni days I had a math lecturer who stated that it was a matter of great pride to him that all the math he created was pure and had absolutely no practical applications. With this in mind what does usefulness has to do with truth? Alternatively, his results where doubtlessly useful to other mathematitians in their research, does that make them more true?