Zero being even is not contentious. Contention is when there is strong disagreement whereas people who are misinformed can be mathematically proven to be incorrect.
By your reasoning you could call all higher mathematics "contentious" because laypeople would come to wrong conclusions due to inexperience. It devalues the word.
OK, if you're going to be prescriptive, I'm going to be prescriptive too.
https://en.wiktionary.org/wiki/contentious
"1. Marked by heated arguments or controversy."
There are heated arguments about this (among laypeople). The people arguing heatedly happen to be wrong, but the dictionary doesn't say that the heated arguments must have merit, only that they happen.
BTW, your "There is literally no credible argument why 0 would be considered odd." suggests that you didn't read the linked Wikipedia page and didn't look at the results of the Mastodon poll. Take a look what actual laypeople self-report about their position on this issue.