Most search engines have regional or country versions. For example, Google has many (eg google.co.uk, google.ca, google.com.au, etc) . If a searcher chooses the [search from country] option, the search engine has to apply a filter to decide which sites are from that region or country to rank them. There are number of possible ways that they could do this:

Most of the decision making weight is given to (1) and (2) and it is not known how much, if any, search engines actually give weight to (3), (4) or (5). Sometimes its the physical location of the server that appears to be more important, but sometimes its the top level domain that appears to be more important.

It is not uncommon in forums to see people confused as to why they do not show up in searches from a particular country. In most cases, it is because the physical location of the server is not in the country. Also, for example, some UK web host companies may use servers based in Europe and some Canadian and Australian web hosts may have servers based in the USA (they may be resellers for another hosting service).