Perhaps you're right. I have tried to find reference to this in the Oxford dictionary, and other sources; but to no avail. I could only find U.S.A. references. Strangely enough though, this is a term which was used in my home in the UK, and among the people we knew. Another term which was used was "kettle holder". It could have been American influence - what do I know! As a point of interest, what did you call "pot holders" otherwise?
Where I live they are called hot pot holders, not potholders. hot pot holders should be accepted. They keep you from burning your hands on hot pots and are pieces of cloth or knitted squares or circles. They look like this: http://1.bp.blogspot.com/-byfAWmYKLak/T2edfXoBcpI/AAAAAAAAEFQ/Lcmj_uMnbik/s1600/potholder5P.png Often they are knitted and look like this: https://i.pinimg.com/736x/fe/10/e1/fe10e14d111f0f4fcedc84be71c52001--potholders-dishcloth.jpg or sometimes people get fancy like this: https://i.pinimg.com/originals/ae/fb/b7/aefbb739734419b456c1d35af67b98db.jpg Look up hot pot holder in google and you'll see tons of them. Hot pot holder is a common word here, but potholder is not, as you don't need them unless the pot is hot. Hope this helps.