Yes Pashtun Sikhs do exist, some have always been Pashtun others are of Punjabi descent.
Just as some Punjabis converted from Hinduism to Islam and Sikhism...
...The Pashtun Buddhists/Hindus/Pagans also converted to Islam and Sikhism centuries ago.
Like Punjabis and Arabs, Pashtuns haven't always been Muslim.
Religions such as Hinduism weren't just limited to Punjab or South-Asia, Hinduism actually came from that direction (Central Asia).
During the Sikh rule of punjab, many muslims converted to Sikhism.
Bull Feces!
To Pashtuns Islam is more dear than their lives, a Pashtun Muslim would never forsake his religion to appease anyone.
A Pashtun bows his head before no one except Allah.
The Sikhs did persecute Muslims during the rule of Ranjit Singh and some Pashtuns did move from Peshawar to the rural areas but none would leave Islam.