Is it normal after foot surgery for dissolving inner stitches to get infected in incision spot?

No: It's not normal but sometimes the degradation of the suture material can be mistaken for an infection. It may be something as simple as the soft tissue reacting to the breakdown of the suture.

Stitches: Sometimes the body tries to expel the inner sutures called spitting. As this forces it's way through the skin there can be a localized infection. Always see your surgeon for any and all concerns.

"NORMAL?": It's not normal, but certainly a possibility. Did you follow your surgeon's post-op orders?