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ByDistance looks very ad-hoc. If you move dist to Point (where it really belongs) as a member function, ByDistance is not required at all, e.g:

 temp.erase(remove_if(temp.begin(), 
 temp.end(),
 [&reference, distanceThreshold](Point& p){
 return reference.dist(p > distanceThreshold;
 }),
 temp.end());

and

 sort(temp.begin(), temp.end(),
 [&reference](const Point& p1, const Point& p2) {
 return reference.dist(p1) < reference.dist(p2);
 });
 );

I don't see a need to create yet another vector with

 vector<Point> result(sz);

You may reuse temp with temp.resize() instead.

Mandatory advisory against using namespace std.

ByDistance looks very ad-hoc. If you move dist to Point (where it really belongs) as a member function, ByDistance is not required at all, e.g:

 temp.erase(remove_if(temp.begin(), 
 temp.end(),
 [&reference, distanceThreshold](Point& p){
 return reference.dist(p > distanceThreshold;
 }),
 temp.end());

and

 sort(temp.begin(), temp.end(),
 [&reference](const Point& p1, const Point& p2) {
 return reference.dist(p1) < reference.dist(p2);
 });
 );

I don't see a need to create yet another vector with

 vector<Point> result(sz);

You may reuse temp with temp.resize() instead.

Mandatory advisory against using namespace std.