Tums...wtf?!?!

Ok so this whole time I am told tums are safe to take for heartburn during pregnancy. I just came across online stating tums are safe but in the same sentence they are considered a category C drug during pregnancy. Wtf!? I would never have taken them. I would rather stick with category b . I am upset and mad that I was told these were safe by obgyn. Am I overreacting??