He said more than that, though. They're probably following the other Jesus who called a foreign woman a dog, along other things. Let's take a closer look.
Jesus fails to "turn the other cheek" and instead gets violent: https://www.biblegateway.com/passage/?search=Matthew+21:12-13
He threatens eternal torture in fire to anyone who doesn't accept his teaching:https://biblehub.com/matthew/10-28.htmhttps://biblehub.com/matthew/7-19.htmhttps://biblehub.com/matthew/13-41.htm and https://biblehub.com/matthew/13-42.htmhttps://biblehub.com/matthew/13-49.htm and https://biblehub.com/matthew/13-50.htmhttps://biblehub.com/matthew/25-46.htmhttps://biblehub.com/mark/16-16.htmhttps://biblehub.com/luke/12-5.htmhttps://biblehub.com/john/3-18.htm, etc.
He kills a fig tree for not bearing fruit that he knew was out of season: https://www.biblegateway.com/passage/?search=Mark+11%3A12-25
He endorses racism: https://biblehub.com/matthew/15-24.htm
When a gentile woman begs for his help he calls her a dog: https://biblehub.com/matthew/15-25.htm and https://biblehub.com/matthew/15-26.htm
He plays favorites: https://www.biblegateway.com/passage/?search=mark+4%3A10-12
He destroys a village's livelihood: https://www.biblegateway.com/passage/?search=Matthew+8
He teaches Christians to have a persecution complex: https://biblehub.com/matthew/5-11.htm
He teaches thought crime: https://biblehub.com/matthew/5-28.htm
He disputes the concept of personal responsibility: https://biblehub.com/matthew/6-25.htm
He condemns skepticism: https://biblehub.com/matthew/14-31.htm and https://biblehub.com/john/20-27.htm
He teaches self-harm in the cause of religious purity: https://biblehub.com/matthew/18-8.htm
He sends his disciples to steal a man’s donkey: https://www.biblegateway.com/passage/?search=Luke+19%3A29-34
He was not a peacemaker: https://biblehub.com/matthew/10-34.htm
He was divisive: https://biblehub.com/luke/14-26.htm and https://biblehub.com/luke/14-33.htm
He was a liar: https://www.biblegateway.com/passage/?search=john+7%3A8-10
So please answer the question: what evidence do you have that these people aren't "Christian?"