Not that strange. Adult-onset T1D is just as common as Juvenile-onset; it just happens to often get misdiagnosed as T2D.
Both T1D and RA are autoimmune, so it's not surprising they showed up around the same time. He was probably infected with a virus a few years earlier which caused the production of auto-antibodies; Epstein-Barr and CMV are famous for this, and it takes a few years for enough damage to take place that symptoms show up. (Symptomatic T1D starts at around 90% beta cell loss.)
Both T1D and RA are autoimmune, so it's not surprising they showed up around the same time. He was probably infected with a virus a few years earlier which caused the production of auto-antibodies; Epstein-Barr and CMV are famous for this, and it takes a few years for enough damage to take place that symptoms show up. (Symptomatic T1D starts at around 90% beta cell loss.)