Hmm , just a short check on wiki claims < note the use of the word 'claims'
Tin oxide for metal oxides ... Hmm , no idea .
Metal film resistors are usually coated with nickel chromium (NiCr), but might be coated with any of the cermet materials listed above for thin film resistors. Unlike thin film resistors, the material may be applied using different techniques than sputtering (though that is one such technique). Also, unlike thin-film resistors, the resistance value is determined by cutting a helix through the coating rather than by etching. (This is similar to the way carbon resistors are made.) The result is a reasonable tolerance (0.5%, 1%, or 2%) and a temperature coefficient that is generally between 50 and 100 ppm/K.[7] Metal film resistors possess good noise characteristics and low non-linearity due to a low voltage coefficient. Also beneficial are the components efficient tolerance, temperature coefficient and stability.[5]
NiCr ? Not much of a idea anyway .
I tried your theory and yes , they all stick , my metal film , carbon film , all of them stick .
I have a odd 5% resistor in a blue case . Hmm . It sticks too .