> This is plainly not true.
Which part isn't true?
There's an online corpus of the Russian language [0], whose entries of usage of the word Urkaine date back to the 17th century — you can easily see which preposition that word took throughout centuries. If you search through books on Russian grammar on Google Books, you will find examples specifically prescribing the preposition "на" throughout the 20th century.
The whole controversy about the preposition started somewhere around the year 2000, and quickly became political. For a disinterested Russian, who is not into politics, "на" would be a natural preposition to use with this word simply because he would have encountered it in classical literature, in the movies, or on TV. It was semantically charged only for those who were aware of the debate. The response from the linguists used to be that if Ukraine wants to use the preposition "в", it is free to do so for the Russian language spoken on its territory; but that it should have no say on how a language is used in another country.
I understand that in the recent years the usage of this preposition has become a political shibboleth; but I am not speaking about it from a political angle. My points are that the usage of this preposition, with this word, in Russian, is 1) historical, and 2) to those who aren't making a political statement, semantically neutral (i.e. it does not, in itself, connote derision, imperial ambitions, or anything of the kind). I have not made any claims about the Polish language (other than that, to my knowledge, it doesn't have articles).
[0] - https://ruscorpora.ru/