The toilet is equipped with a plastic water tank with a PVC pipe. Although PVC was first discovered in the 19th century, and found its first commercial use in the 1930s, it was still quite rare. A Budapest apartment in 1950 would've had a porcelain water tank.
A Bensdorp cocoa can is repeatedly seen in the pantry. This packaging, the "Smiling Woman" only appeared in the 1970s, and it's pretty much a staple of its era. In the 1950s and before, Bensdorp cocoa came in rectangular cans, with a different image of another woman in traditional Dutch headgear.
As the State Security agents march up the stairs to the apartment, a small, rectangular grill is seen in the wall, well above head level. These grills were installed over air ducts in old buildings during 1980s.