John Gill Commentary 2 Samuel 19:2

"And the victory that day was turned into mourning unto all the people; for the people heard say that day, The king grieveth for his son." — 2 Samuel 19:2 (ASV)

And the victory that day was [turned] into mourning unto all
the people
They also mourned too, instead of expressing joy upon the occasion:

for the people heard say that day how the king was grieved for his
son ;
this report was spread among them, which damped their joy, and hindered them from giving any tokens of it, as were usual at such times.