Stuff like this is why we get parents claiming that teachers are trying to indoctrinate children.
Seems like a loose definition of indoctrination... is any teaching indoctrination by your definition?
Here's a simple heuristic: if a teacher presents a false proposition as truth, is corrected, and has the epistemic humility to revise what she teachers, she's not indoctrinating.
A student would have an easier time disproving the Pythagorean theorem, the Heliocentric model or even the history of slavery than convincing these teachers that they were wrong. The former claims are all at least contingent on evidence.
Read this article carefully. At every occasion, she is projecting her beliefs and judgments onto the children. There is no amount of evidence that could falsify her conclusion. It's pure, unadulterated blind faith. Whenever the kids reject the teachers' assertions, the objection is categorically interpreted as evidence of how "ingrained" into the kids' psyches capitalism, inequality and the rest of the parade of horribles are. Pay particular attention to how "Drew" is framed, the kid who evidently was a leader in this group. He's very hesitant to accept the teachers' judgments, and only does so after significant argument. When he does, he is praised for toeing the Party's line, and shortly thereafter the kids are given the legos back, with significant restrictions. Again, these are framed as if the kids actually agreed to "all houses must be the same" (I almost want to try to impose this rule on my kids - I imagine I'd be stepping on many fewer Legos, though time vegging out in front of Netflix would probably increase). But given all of the other admissions against interest that the author makes (including that the teachers didn't want to impose authoritarianism and so they took the legos away), I imagine these were not at all open-ended discussions, but were strongly manipulated by the teachers to achieve a certain outcome. The author isn't the first socialist to preach the gospel about control over the means of production who nevertheless treats the demos as if they are incapable of managing without her help.