There are two main reasons why teething and infections occur at similar times

Increased exposure to new pathogens: At the age of 6-12 months, infants are suckling and chewing different things while exploring their world by putting things in their mouths. This exposes them to new pathogens.
Antibody loss: When babies are 6 to 12 months old, they start to lose the antibodies that their mothers pass on to them during birth. This means that their immune system has to respond to more infections, such as the common cold.
To summarize, a fever may occur around the same time as the teeth appear, however, a fever is a sign of infection, and is not a normal symptom of teething.