Not necessarily.

In Jain Dharma, sin comes mainly from attachment, aversion, and intentional harmful intent. If you accidentally see someone naked and no lust, attachment, or wrong intention arises, then it is not a sinful act by itself.

But if one deliberately looks, entertains desire, or allows the mind to become impure, then it becomes harmful to the soul.

So the simple answer is:

• Accidental seeing without desire: No
• Intentional looking with passion or attachment: Yes

In Jain conduct, the focus is on purity of intention, restraint, and control of the mind.