After a technical article was published online without applying for a patent, someone plagiarized it and applied for a patent. Does the former publisher infringe the latter's patent?

No, the patent is invalid because the technology has been disclosed before the filing date and is no longer novel.

Article 22, Paragraphs 1 and 2 of the Patent Law:

Inventions and utility models for which patent rights are granted shall possess novelty, creativity and practicality.

Novelty means that before the filing date, the same invention or utility model has not been published in domestic or foreign publications, publicly used in the country, or otherwise known to the public, nor has the same invention or utility model been published in domestic or foreign publications before the filing date. The invention or utility model has been applied for by others to the patent administration department of the State Council and is recorded in the patent application documents published after the application date.

Article 23 of the Patent Law: The design for which a patent right is granted shall be different from or similar to the design that has been publicly published in domestic and foreign publications or has been publicly used domestically before the filing date. , and shall not conflict with the previously acquired legal rights of others.