There is no such thing as basic grammar, FFS. If you knew what they meant then they conveyed their meaning perfectly and you are being needlessly rude. Unless you are grading a paper that has specific requirements for Standard American English™ there is absolutely no reason to be a cock about someone else’s perfectly expressive language.

Yale Grammatical Diversity Project: https://ygdp.yale.edu/project-description

https://www.bbc.com/worklife/article/20210528-the-pervasive-problem-of-linguistic-racism

https://www.theparisreview.org/blog/2020/01/07/the-limits-of-standard-english/

https://web.stanford.edu/~zwicky/aave-is-not-se-with-mistakes.pdf

Language and Discrimination: Generating Meaning, Perceiving Identities, and Discriminating Outcomes: https://www.annualreviews.org/doi/10.1146/annurev-linguistics-011718-011659

“we regularly demand of people that they suppress or deny the most effective way they have of situating themselves socially in the world”—their language (Lippi-Green 2011, p. 63). Institutional function often depends on a particular set of beliefs about how language, especially the standard language, works. Lippi-Green and others refer to this set of beliefs as the standard language ideology, defined as “a bias toward an abstracted, idealized, homogeneous spoken language which is imposed and maintained by dominant bloc institutions and which names as its model the written language, but which is drawn primarily from the spoken language of the upper middle class” (Lippi-Green 2011, p. 64; see also Agha 2007).

See also: Prescriptive vs descriptive grammar and the uselessness of the former.