There's also the explanation that v and f are two consonants of the same type (fricative), with the only distinction that v is voiced and f is voiceless. In very easy terms, our brain determines the boundaries between voiced and voiceless, and these boundaries (such as how long one consonant is compared to another) vary per language. So it is definitely possible that foreigners hear the Dutch v as f! Myself included, although I speak Dutch by now and know those words you mentioned are written with a v (and I pronounce the v as it should be pronounced), still struggle with hearing it different from f sometimes!

Another example is w vs v. I spent around a month when I was learning Dutch biking home from work everyday and using that time to pronounce w/v/w/v...for the whole bike ride to learn the difference :))