Alternative to Silicone Wood Filler for Door Frame
The flooring is supposed to extend far enough under the door trim molding so that no sub-floor is visible.  The gap you have is non-standard and is completely unacceptable.

Presumably you have some scraps of flooring left. The installer should scrape out the filler and insert a piece of flooring into the gap.

EDIT

To be able to work in the scrap of flooring, the installer might have to cut off a small amount (say 1/8") of the door trim, but this would be inconspicuous.