Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

It is absolutely necessary for Muslims to clean themselves after using the toilet. This can be done with either water, a solid object like toilet paper, or both.

During the time of the Prophet Muhammad (peace be upon him), the Companions would either clean themselves with water or stones [since there was no toilet paper].

The purpose behind using these is to make the area as clean as possible.

If using both causes it to be more clean, then it is recommended to use both. Perhaps these Muslims are concerned that some people think it is a requirement to use both, or that the Prophet and the Companions used both.

As long as you do not believe that it is a requirement then it is not bid`ah. Perhaps they did not use both due to scarcity of resources, or perhaps they did combine both but we do not have a report that clearly states that they did.

Either way, this should not be something that is made into an issue which will divide the Muslim community and cause them to disagree. Whatever cleans the area better is fine to use.

Almighty Allah knows best.