Normally a T1 will have lost all beta cells (and therefore insulin production) after a year or so post-diagnosis. However there are some rare cases where several years on, a T1 still retains some active beta cells, so still produces a very small amount of insulin. Possibly enough to keep blood glucose levels in the 15-20 range? But very rare.
Bad idea being taken off insulin completely. Metformin in a T1 so affected isn't going to do very much, except perhaps increase the body's sensitivity to the insulin that IS being produced naturally and/or burn out those remaining beta cells more quickly? Change doctor quick or at least get a second opinion!