Ref. No. 39 / 0000
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
The non-Muslims also come under the Ummate Mohammadiya (saws) because the Prophet Mohammad (saws) is a messenger sent to the entire world till the Day of Judgment. The Ummah are of two types. (1) Those who accepted Islam and they are called "Ummate Ijabat" (2) Those who did not yet accept Islam or became disbelievers and they are called Ummate Dawat (they are to be invited to Islam).
And Allah knows best
Darul Uloom Waqf Deoband